Late period with a twist

I'm on day 37 of my cycle. I often have a longer cycle.
 my boyfriend came inside me about day 24/25 because I thought I would be getting my period soon. Day 31 came and still no period so I freaked out and bought a test that said I wasn't pregnant. However why have I still not got my period. Could it have been a faulty test? I have had the flu around the middle of my cycle and I've just got it again yesterday so I'm not sure if sickness has had an impact or not. 
I'm aware I usually am late but he's never come inside me before so it's playing with my head a little. Any tips would be really helpful.