how do you no if your pregnant

rite I have always had unprotected sex, I no Iv had one miscarraige and I think I may of had 2 but whenever i have done a pregnancy test it has come up negative and I didnt realise until earlier on today that PCOS can affect the results.

so since monday I have had ery light pink discharge in the mornings which is on and off and it seems like by the end of the day its brownish so i been looking at the internet and im concerned I may be pregnant. Iv had lower back pain but i dont no if that is from the work i do and over the past 2 days iv almost had an aching pain only subtle where my womb would be. im looking for answers really as i rang the doctor today and they said if a hcg is negative then ur not pregnant which i did break down and cry after that conversation because i want to no 100% whats going on.

can anyone give any help advice etc on my situation please