need advice 5 days late

Now the last few months have been so weird with my period. In October i didn’t get one at all, and in November it came super late and didn’t last very long. Same with december. I didn’t think anything of it because girlfriends gets theirs around then so i figured we were all syncing up. But they got their periods, and or already had their period and it’s over. So i’m not sure what what could be happening. My one boob hurts, it gets these pains in it. And every single morning i am nauseous and my belly hurts. I haven’t really had an appetite (not due to nausea, it usually goes away after i go to the bathroom) i just haven’t been hungry. and usually i’m stuffing my face on my days off. I wanna go buy a test but i don’t want to waste it. I wasted like 30 bucks last month because she was late. My boyfriend came in me every single month multiple times in October-December we’re not trying to get pregnant but we don’t mind. He only came in me once this month.