Hi and thank you for sharing your question with the EmpowHER community.
If you have endometriosis, one of the most common symptom outside of pain is menstrual irregularities. What symptoms are you having to make you feel like you are pregnant?
More than likely, your 2 days in January was an irregular period, but it sounds like you need to be reassured. The quickest solution is to do another HPT to confirm your results from December and go from there. If you are still not comfortable, I would call and discuss with a nurse at your OB/GYN's office.
Perhaps someone with a similar experience will provide input, but ultimately everyone is different.
I hope this helps.