Remeron versus Lexapro

I am trying Remeron for depression but have had the opposite side effect for sleeping. For the first few days it did help with sleep but now I can’t get to sleep, toss and turn, get up and walk around, watch TV, and try to read but nothing seems to help. I am considering going back to Lexapro as I have been on it before and it worked well. I am also concerned with the comments about weight gain.