Could I be pregnant???

So December the 8th I gave birth to my second child and went to the 8 week check up and got my pill but since my son has been born we haven't used any contraception and well on my fertil week we didn't use anything now I'm worried but with my first it was wired I had one period after she was born and for four months didn't have a period but weren't pregancy then took the pill and my periods came back could it happen again? And could I be pregant?