freaking out...tubal ligation.. pregnant?

I had my son Feb 1 he's 9 weeks old. I had a tubal ligation the next day(done the clamps). 4weeks Dr says everything looks great, at 5 weeks I have sex with my baby daddy who I would out at 8 weeks was cheating on me. he's moved on completely only talks to me concerning our children other then being completely devastated, I've been spotting for the last two weeks. I've yet to have a perios, took a pregnancy test it was negative but I haven't given it enough to time for the last time we had sex to even show up on a test. I'm completely freaking out cuz I have the signs like I have with the last three babies. I don't want another child hince why I got a tubal, I'll take responsibility if I have one but I'm not sure he'd believe me. he'd prob think I'm just trying to split them up. how many woman have had a tubal with sytoms like this and not be pregnany