Hey mama! Balakang pain is super common in early pregnancy kasi ang ligaments mo are stretching na, pero since you're only 7 weeks I'd really suggest checking with your OB pa rin para ma-rule out other things at ma-ease your mind, a few of us moms went through similar and iba-iba ang cause, so better safe talaga. In the meantime, take it easy, try warm compress, at don't carry heavy stuff na muna. Wala naman sa UTI based sa urinalysis mo which is good, pero your doctor will know best kung ano talaga ang nangyayari. Ingat ka always, mama!