Sudden Sleep-Onset Insomnia?

I (23F) have been having some serious trouble sleeping the past several nights, seemingly out of nowhere. I fall asleep fine, but about 20 minutes later, I wake up and can't go back to sleep for about two hours. During this time, I also get up to pee several times. I've never had issues with needing to pee at any point in the night before (and don't during the day). Last night I ended up taking a benadryl, which worked but still took a while. My body is tired but my mind won't stop ... I don't even feel anxious per se, I'm just thinking. Any ideas would be appreciated!