So I want to do a brief background story

I'm 28 years old

I have endometriosis stage 2

I have a six year old son born via c section

I'm currently 7 days late for my period

I was previously taken the mini pill which in stopped half way through January due to it affecting my mental health

My last period was from 30th December to 4th January and my cycle days are between 28-30

I'm currently experiencing constant headaches, neasea,mild pelvic pressure, tiredness, sore boobs,backache,hip pain

I've had HCG blood test today at the doctors and I've taken a cheap pregnancy test which struggled to process and it ended up being negative (don't know if I believe it) what does anyone else think is happening? Should I believe the cheap pregnancy test? Is it just my body playing tricks on me?