Hi Leno! I am now 13th week of Lexapro (mostly at 10mg) and had very similar start up and set back experiences as yourself (sporadic bad days). Around week 9/10 I was feeling decent but noticed a sudden onset of jaw clenching and slight headaches. With approval from my DR, I dropped down to 7.5mg for a week and the new side effects subsided. Unfortunately for me, I had my first panic attack in weeks after a couple days on 7.5mg and realized I wasn't quite ready to lower my dosage yet. I started taking 10mg again in week 11 and have been stable back on 10mg since. I don't want to jinx myself, but I've felt better these past two weeks than I've felt in months - zero bad days and this says ALOT considering all the holiday stress I've been under PLUS I have super bad PMS anxiety and that was completely muted this past week, as well. Everybody says to wait 4-8 weeks but even at 8 weeks my good days were not as consistent as I would have liked. I know everyone is different, but I'm hoping a couple more weeks will bring you more stability as it did for me. Plus if I remember right, you are only on 10mg so you can also discuss upping your dosage with your doctor if you feel its necessary.
For me, personally, I think the dip down to 7.5mg was exactly what I needed to get my head right about the medication. Its hard to realize all the progress you are making when you are still having bad days here and there. I was having a hard time accepting the fact that I needed the meds and wasn't convinced they were really helping. When I went down to 7.5mg for two weeks, I was able to use my new coping mechanisms to managing the increased anxiety the majority of the time, but the panic attack was enough to remind me why I wanted to get on the meds in the first place. I realized in that moment how much the medication had helped in the past months by simply eliminating my panic attacks. There was no hesitation what so ever bumping back up to 10mg the next day after that and I'm normally freaking out about any medication changes. I'm not recommending changing your dosage by any means 
, I just think a lot of my personal struggle was because I was focusing on the negative more than the positive which made me into a complete head case about the medication :)
In regards to my dosage changing.... I was only on 7.5mg for two weeks but experienced ZERO withdrawal or start up side effects bumping down to 7.5mg then back up to 10mg. Just wanted to share what a relief this was since my initial increase to 10mg was so difficult. I'm sure getting off the medication all together might be more challenging when the time comes, but I feel more confident about tapering knowing I had no ill effects going down 2.5mg at a time. Figured I would share this fun little tidbit in case you are like me and have read all the nasty things google has to say about Lexapro withdrawling :)