How Do I Know If the Meds Are Really Working?

Hi, I slowly went up to 10 mgs of lexapro about 1 month ago and really started to feel like myself again for about a week, then I got really depressed again... :( then I took 15 mg for a week and now i'm on my first week of 20 mg. Sometimes I feel as if i'm getting better but sometimes not, how long should it take to feel myself again, is this normal?