SUPER LATE

So I’m 13 days late for my period, but haven’t had sex in 2-3 months so I really don’t think I’m pregnant. I have consistently been having kinda unstable periods, like they’ve been late for 5-10 days, and my cycle has been getting longer but never this late. I did have a period last cycle but right now I’m on cycle day 50. My cycle is typically longer, 35-40 days. My boyfriend and I have been messing around, but not enough to get me pregnant in my opinion, meaning we haven’t come close to sex or him ejaculating near my vagina. I’ve also been really stressed because of final exams, but I haven’t missed a period in 3ish years. I don’t have any symptoms one way or another. What should I do? It’s so hard to convince myself to buy pregnancy tests. I’m also about to leave home and go abroad for a month so I’m nervous about that too.