Just my thoughts:
1) While I have also read that green tea seems to make some people lose weight (because it seems to curb appetite), I've been drinking it for some years without marking any weight loss. I would not look to green tea to help you lose weight. The studies making that connection are not very steady
That being said, studies have proven a much better connection between it and healthy markers (lower chance of cancer, less heart disease), so you shouldn't not drink it just because it probably won't cause you to lose any weight. What's more, it does have a bit of a taste, so people that are adverse to plain water may find that it a better alternative, especially if they need to drink more fluids.
Like I said, I've drank green tea for several years now and it doesn't bother my IBS. I do have a problem with caffeine bothering my IBS. A few points, though. One, decaf green tea--while available--seems to have less beneficial properties than green tea with caffeine; probably because stripping out the caffeine or doing whatever it is to make it "natually" decaffeinated also makes you lose some of the healthy things that are in it. So, I drink mine caffeinated. The reason why I can do this, though, when I cannot drink caffeinated regular (black or oolong) tea at all, is because I don't make my green tea very strong. Too many people make their green tea WAY too strong. This is supposed to be a very subtle taste; a lot of people complain that properly-made green tea doesn't taste any different from water. As someone who drinks nothing but green tea and water, I can tell you that it does have a taste to it, but, indeed, it's nothing like the taste of regular tea.
Here's how I make my green tea: I take a tea pitcher and fill it up with hot water from our kitchen tap at work (that water is hot enough to scald). Hot water from a water dispenser or coffee maker is also plenty hot. Green tea is one of the few teas that you should not steep in boiling water. When I have my tea pitcher full, I stick in two bags of tea. The best tea I've had was some imported from Japan that my husband got for me from an international market, but that's way out of our way, so I usually make do with just Salada's green tea. It's not wonderful green tea, but I've definitely had worse. It's a decent tea at a better-than-imported price and can be found in any grocery store, so that makes it a winner in my book.
Note that I only put in two bags. If you read the box, you'll see that they say 1 bag for every 8 oz, which would be 8 bags of tea for a tea pitcher. This is way, WAY too many tea bags. Really, really good Japanese green tea is a very light neon greenish-yellow color. It's actually rather bizarre-looking in color. Salada tea makes a very light golden/honey color (with maybe a hint of green tint to it) when properly brewed. If your tea is approaching brown in color, it's too strong. The problem with tea that is too strong is that it 1) has more caffeine in it (the only reason why I can do green tea is because I keep it light), and 2) it's bitter. If you sip your tea and think it bitter, then you've made it too strong; try watering it down. There should be no need to add sugar or anything else to your green tea.
Because I only use two tea bags, I don't have to carefully time my tea (a bonus since I drink all of this at work and am too busy to watch a clock). I just let the two bags steep in the pitcher for as long as they want (this also cuts down on wasting tea bags by dumping 8 in and leaving them only a few minutes, thus leaving a lot of tea still stuck in the leaves). In fact, I don't even bother to remove the bags. I guess I let it steep at least 5 minutes, but I've been drinking it so long now that I gauge it's readiness by the color (needless to say I have a clear tea pitcher). There's only so yellow it will get before it stops getting any stronger, and that's when you know that it's done.
I would not put any citrus in my green tea because 1) it's not necessary to flavor it and 2) citrus doesn't like me very well, so I need to avoid it. I would suggest that, with IBS, you avoid it too.
If you have tried drinking green tea from a bottle that you bought in a store... well, you've been ruined! I've had that stuff and it tastes nothing like the green tea I make for myself. In fact, it tastes like a bunch of other junk instead of green tea. I used to be a coke-addict and now I drink pure, unadulterated green tea. That means anyone can learn to drink it that way. 
2) While you can certainly try to take more probiotics during "that time of the month" I don't know if they will do any good. Your problem then are with your hormones, not your bacteria. I used to get constipated before my period too; that or D happens to a LOT of women, especially (althought not exclusively) to people with IBS already. Some women here who have C with their periods say that when they know it's coming, they up their fiber intake a bit to help combat the C. You might try that.