False negative ?

Has anyone ever had a false negative while on thyroid medication due to hypothyroidism? My lmp was 3/14, all my tests have been negative, but for the last two weeks I’ve felt my pelvis weaker and crampy? Which is similar with what i felt with my previous pregnancy. I’ve been on thyroid meds since January, so not sure if it’s just due to that. Your advice would be helpful, thank you!!