Pregnancy

Me and my boyfriend have been trying to have a kid for almost a year now. He has a one year old daughter of his own from a time where we weren’t on the best of terms (no he didn’t cheat). We’ve been dating off and on since are 8th grade year of school and have yet since graduated. We both want a kid together as we’ve been trying for some time now. I always think I’m pregnant as my boobs start to swell then hurt, but then a couple days go by and their back to normal. I am sometimes 4-5 days late then sometimes a week or longer late on my period.Here lately my periods have been around the same time with a day or two difference. Any tips on what to do or how to help. I haven’t been to a doctor because I figured I’d see what could happen since nothings seriously wrong, but should I go get checked or maybe him. I mean he has a kid already though, so idk what to do. Could stress cause a problem with that as I do stress about his daughter, because we are like high-school lovers and I’d never think he’d have a kid with someone else, but he didn’t know either until after her first birthday. I NEED HELP!!!😭💔