Help meee I'm so ashamed of myself

Well let's start by saying, I am pregnant and my due date is May 8th, according to ultrasound, it came to a surprise to me, because I'd been on the pill, well my ex and I of four years had broken up on September 1st, I made a drunk mistake and slept with someone else on September 8th.. can somebody please tell me that it's my exes!? I can't remember the name of the random stranger I'd hooked up with, and also I been tested already, in September and also in January, I'm clean thank god! But also ashamed, I have not slept with anyone else since then and even then the only person I slept with was my ex.. anywhoooo advice ladies? Thanks so much for not judging me!! 💕😣