Most of Lexapro's side effects seems to be physical rather than mental, but regardless; whenever you have a shift in your daily mood that becomes so periodic that you notice it, you need to discuss that with your Pdoc. There is a chance your body has become tolerant to the medication, which is what happened to me with different meds. There's a chance the welbutrin is messing up the way the Lexapro is supposed to work.

It could be because of different situational things in your life that make the peace of nighttime just easier to bear, in which case you would still need to address that with your T and Pdoc because taking meds without them seeming to work is a problem none of us want.

TLDR; it is very possible your meds could actually be hurting you rather than helping, even if it doesn't happen in the first five weeks when side effects are most prevalent.