4 days late and negative result

hi i was wondering if anyone could help me out, my last period was 3rd December which was my normal 5day period, i had alot of unprotected sex then from the 17th to the 19th December, on 22nd December i had a little pinky/brown discharge which then got heavy but went away day 3, since then i have been feeling so tired  cant get enough sleep, mild cramping and lower back pain here and there my next period was due 29th dec and today i am 4 days late no period, done test and negative. on the 29th i did start spotting instead of period, its a really light pink colour and only when i wipe, does not fill a sanitary towel or anywhere close to filling it. if i was pregnant i would only be 2 weeks so wpuld it be too soon to get a positive result or could i just not be pregnant