PERIOD DELAY. Get a pregnancy test done?

Hello there. I'm all new to this so apologies if I'm being too specific but I'm in dire need for your help. I had unprotected sex on the 14th right (2-3 days after my period completed) and I took the morning after pill within 18 hrs of the sex. After a week I bled heavily for 2-3 days and stoppe later. so far I've had terrible lower back pain for a 2 weeks in the begging of march and extreme discharge recently (from mid march). I got myself an sti test done recently but that is not part of my problem. my period is usually fue around 7th and I've yet not received a proper period except for 2 days around the 7th I spotted. I haven't considered that as a period as it was extremely light than my usual period and it was just spotting. it's been 3 and a half weeks since I was supposed to have my period. could you please help me? am i pregnant? do i need to get a pregnancy test done? hope to hear from you soon xxx