I think I am pregnant with my Ex boyfriends child.. What to do???

I've been gaining weight rather quickly the past couple months, I feel like it's way too fast. At first I thought it was just because I started nursing school and I was stressed but now I'm not so sure that's what it is. The past few mornings I've been waking up around 2-3 am feeling so nauseous having to run to the bathroom. I did have my menstrual bleeding this past period about 3 weeks ago. I should be due for my next in about a week but I know people can be pregnant and still bleed. I don't know if I'm worrying for nothing but I'm kind of freaking out.. Besides taking a pregnancy test does anybody have advice for me.? Please and thank you.