I would not do a paternity test it cost money and its just your imagination. When I was 18 like 10 years ago :D I was married to the only boyfriend and only man I had been with in my life and while pregnant I would be worried that my baby was not his. Like maybe I was sleeping and someone broke into my apartment and got me pregnant or I just got pregnant and the baby was not his...thoughts that are so strange because I had not been with another man. Even at birth I was worried...but I was not worried like I was a few weeks back when I really was not sure who the daddy was. I was just nervous like what if. Well the baby was his obviously and looked and looks just like the guy I was married to. So crazyyy. The crazy things our mind sometimes makes us think.
and sorry to answer your question, if you havent been with anyone you dont need a paternity test, but I am all about doing anything that makes YOU feel better. If you want to do so and it will help by all means go ahead.
Wow, it sounds like your boyfriend is a great guy and that you have a very loving and supporting family for your situation.
Im not sure how old you are, but this is a VERY survivable situation. When I first got pregnant at 19 (7 years ago), I had the EXACT same wild and crazy thoughts. I thought "maybe I got drunk and had sex with someone else?" but I DIDNT. Like at ALL. it was a faithful relationship with my boyfriend at the time, but trust me I had all kinds of crazy thoughts going through my head. You are NOT alone!
Its AMAZING what our minds can do to us. I am planning on getting a prenatal paternity testing (before the baby is born) due to my horrible situation i put myself in... try to take a deep breathe, and keep reminding yourself that you did not sleep with anyone else so you have nothing to worry about. Sometimes in my head its like an inner battle where I literally have to talk sense into myself. Its wild!