Dear Doctor My Question Is One Of Gynecologic Type. I

Dear Doctor
My question is one of gynecologic type. I had protected sex three months ago and I am not sure if my sexual partner ejaculated or not. All I know is that half way through he went soft and the condom started slipping but unfortunately we continued. After 20 day my period came 1 day late and instead of red blood that I usually have I had brown spotts that got heavier and then lighter again , this laster 4-5 days and I had tremendous cramps for 2 days something that I never have. In the shower though I think I saw a oocyte. My next period was delayed by 6 days and it was normal slight cramps normal blood but still less then usuall. My period after that came after 19 days and was really heavy I had to change my pad really frequently and my blood was bright red. In general my periods have. never come so early or so late and I have always had blood not brown blood. My question to you is from what you just read could it be that I am I pregnant? Before my first period I took 2 pregnancy tests and they were negative but the differences in my period scare me . I am not in a situation were I can just buy a pregnancy test so this is my only way please help me. Thank you for your time. ( I am a veterinary student so I would appreciate a Scientific explaination) Thank you.