What Could Bleeding Between Periods With Sharp Pain Under The Ribs Indicate?

Hi, last time my period came it was just light flow and brown (no red at all) for about 5 days, then my normal period came after that for the normal 6 days. I went to the doctor and he did a urine test and STD test which were all fine. Now my period has started again (2 days ago) and it s brown and weird again, plus i have sharp pain under my ribs. Would the two be connected? Should i be worried?