On the pill and unprotected sex

I've been on the pill for nearly 3 months, I've taken it relatively around the same time everyday (latest has been 2 hours late but that was only once) I had sex but the condom broke so he came in me. 3 days later there's some spotting and cramping. I was wondering if this was just caused by stress or if it's implantation bleeding? I read that if you stress yourself too much that your body can trick itself into pregnancy symptoms.