Positive OPK? TTC 5months! HELP!!!

Okay so my husband and I have been ttc for a few months now and for the longest I just could not understand why I keep getting negative test. We follow the calendar and still nothing. Lately my periods have been coming earlier but back in July I had a full 30 day cycle they've also went from lasting almost a full 6-7 days to just this last one only 4. I got some OPKS (first response fertility) and I started testing on the 9th. I realized that glow said my fertile week was from the 10-16 so I skipped the 10th in order to not to use to many since I started testing early. Well today the 11th I got what looks like a strong positive for a surge. When I entered it into glow it changed my fertile days to 7-13. I always felt like maybe my fertile days was wrong and maybe I ovulate sooner. So my question is should I keep testing until the 13th or stop to save the test for next month just in case and keep BD anyway?

Extra info I had really bad cramping last night on my lower left side I associated it with gas but I get this pain once a month around the time I'm due to ovulate.