So I've got my first ever late/missed period... could Lexapro be the culprit? Is that even a thing?

So, I'm a week late on my period (something that NEVER happens for me, as I am almost annoying regular when it comes to riding the red wave) and I don't know what's going on! Like most ladies who are having sex and late on their period, I already took two pregnancy tests and they both came out negative, so I'm pretty sure there's no baby in my belly. But, still, I don't know what's going on.

I do have some pretty hefty issues with anxiety/depression. I somewhat recently (in September) switched medications from Zoloft (which I had been on for several years) to Lexapro. My cycle last month was normal, but this month it's definitely out of whack if not coming at all. Could Lexapro be the culprit here? Has anyone had this experience with anti-depressants?

It actually feels like I have cramps right now, but there's no blood is in sight (and I usually have a heavy flow), so that's also strange. Any idea what could be going on? I thought it might be out of whack due to stress (and I have been a little stressed lately), but not more than I have been in the past (and my cycle was still normal then). SOS!