you guys congrats on baby and a medal for already back to having sex! wow!
I looked it up briefly and it looks like you could in theory be pregnant, sorry!
I found this:
"Despite the fact that it is not recommended that you have sex prior to your six week check up, it happens. If you don't use birth control you can get pregnant. Breastfeeding, while it may delay ovulation in some women, is not an effective method of birth control unless you are following the Lactational Amenorrhea Method (LAM).""
tricky thing is that even if your pregnancy test was positive, would it show the hCG hormone present in new pregnancy (so yes, you are) or the leftover from 3 weeks ago (no you are not) can they tell the difference?
also if it shows negative that's just as useless, coz even if you are pregnant it might not show for a few weeks!
I'm sorry, I'm probably making this worse, you'd better talk to gp, get a blood test if possible.
I think after 6 weeks check you can have an early scan (vaginal scan) to see what's what.
maybe best to "hold your horses" so to speak for a bit, until you get a bit more info/advice...or go full steam if you don't mind getting pregnant! (though I'd still wait for 6 weeks check up)