Questions about constipation

I am 66 years old and have posted on here for a few years, as well as on the anxiety/panic site (I sufffer from health anxiety). I have had stomach/intestinal issues since my 20's, with flare ups lasting up to three months, then periods of complete normalcy lasting 2-3 years where I could eat anything without problems of any kind.

I'll admit I am under serious stress, having been laid off before wanting to retire, no insurance until next month, and have serious concerns about finances, etc. So over a month ago I started having diarrhea after anything I ate....sometimes 4-8 times a day. I attributed the diarrhea to taking Zantac because when I stopped taking it, the diarrhea stopped. Only problem is, now I have the complete opposite - constipation which is an entirely new symptom for me. I have always been VERY regular so this new symptom scares me. I can still have a solid bowel movement after alot of trying, but it never feels like I am completely finished and I don't get that strong urge to go like I always used to...I have to "make" it happen rather than letting it happen on its own. I worry about a blockage and wonder if a blockage means the total inability to go or just difficulty in passing stool. Most of my pain and discomfort is from bloating and pain on my left side but sometimes on the right under rib cage near gall bladder (I was diagnosed with "sludge" in gall bladder quite a few years ago). But as I said, sometimes my symptoms would go away for years at a time. Sometimes I feel like my concern over this issue just causes me to "tighten" up and keep me from relaxing enough to go normally but I'm not sure. Is there some kind of natural laxative I can take and what foods are good for normal bowel movements because I don't want to go back to diarrhea again either. Very confused about all of this so any advice would be appreciated.