Worried I could be pregnant again...

Kerry
So my period is a week late, and I'm scared it could be because I'm pregnant again. Our first child is nearly 6 months and I don't know if I can cope with another so soon. We have been using condoms (I can't take hormonal contraceptives) and neither of us is aware of there being an accident but that doesn't mean that there hasn't been. 
I took a test when I was 4 days late and it was negative but then later that day I had a tiny bit of a bleed which I'm concerned could have been implantation which would mean the test wouldn't have been positive any way. On top of that I've also had really bad heartburn today.
I've bought another test and I'm going to do it tomorrow morning but I'm so stressed. I know there's not much anyone can say but I guess I'm just looking for a bit of support. 😕