should I buy a pregnancy test?

I've been questioning myself if I should buy a pregnancy test but I am not sure. In the past I was ttc and every chance I had a pregnant symptom I would go and buy a test which would always come back negative. After months doing the same and getting the same results, I just stop trying. I rather just let it happen on its own. But recently I've been sleeping so much, been so moody and emotional. In August, my period was very short. I usually get it for 4 days and this time it came for 2 days but very light. Not sure if it's implantation bleeding or not. I really don't want to stress it I'm very unsure.. I don't want to be disappointed and get a negative again. So I'm not sure if I should take a pregnancy test or not.. Btw I have PCOS, but I get my period every month.