brown spotting. I need advice

so about a week ago I was giving oral sex he tried to put it in twice but when he did I immediately took it out after that the next day I started feeling strange my stomach was hurting I was cramping every now and since then I been like this and yesterday I experienced brown spotting and then this morning I woke up and I have what I believe is my period But I'm not so sure. I have a heavy flow and it's not heavy but the cramping in the stomach aches are still there too has this happened to you before? im scared.