I'm very worried help a girl out please

so 3 weeks ago I had unprotected sex it was my first time having sex and we had it 4 times that week 😂 he pulled out and didn't cum inside me at all and I'm also on the pill. I did heaps of research and I was pretty sure I wasn't pregnant except I was feeling way more tired than usual and that's it. So my period was 2 days late and it's never ever late since I'm on the pill so I was like that's weird. but then when it did come it wasn't even like a period it was just like a small amount of the brown stuff u get at the end of your period kind of like spotting. I thought that was really weird and it's never happened before. Can someone help me out?