Someone please help me

Alice
I'm on the contraceptive patch I have been on it for a year and a half I've never had any problems until now. I started my patch free week on the 24th and put my new patch on on the 1st of march. My patch fell off and I didn't realise until today I had sex on the Saturday all of a sudden I've started to bleed and have terrible tummy cramps and pressure in my back my periods are never like that I'm not bleeding heavy but it's fresh blood. I really don't know what to do I'm in so much pain I've tried paracetamol nothing's working I'm really worrying 😔