Really confused right now

My partner and I were having sex and the condom fell off inside when he pulled out (embarrassing I know) anyway when I got the condom out there was hardly any of his stuff in there.. This would have been three weeks ago that this happened and I've been getting a few symptoms, but I took a cheap pound land test and there was a faint line and today I bought a clear blue digital and it said that I wasn't... Can somebody explain this.. Should I wait a few more weeks and try again? Please help ..