I'll be buying a 5th pregnancy test soon

I gave birth 6 months ago and I'm exclusively breastfeeding. I don't use birth control since I react to synthetic hormones and copper. My husband and I messed up a couple times and had sex with no condom. It's our third baby and we are exhausted.

Now the last month I've been extra tired, my face is breaking out like crazy but my tests are negative. Calculation of conception give me a wide window of 9 weeks to 12 weeks. I'm so scared