To start off I was on the pill and it was placebo week, my period never came it's late 13 days i've been feeling very tired nauseous and I've been spotting I took so many pregnancy test, all negative I went to the OB/GYN and they did another pregnancy test by urine and he said I'm not pregnant and that I had a UTI

he told me that it could be too early for it to show up on a urine test, and that I should take another test in 10 days (which was 4 days ago)

so I've been taking my anabiotic's for that and the pain from UTI went away

but still no period and now I'm having some thick discharge and I've read online that that is a sign of pregnancy with the spotting which I had spotting but then had heavy discharge

Can somebody please help me to understand how early pregnancy works and if it's possible that I am pregnant?