Should I test again ?

I took a test on the 15th at night and on the 16th with first morning urine (6 days late). Both were negative. Do you still think it’s a possibility to be pregnant. Only symptom I have is lower abdominal cramps and back cramps which is normal when I’m getting me period. but it hasn’t shown. Back in September I missed my period for the entire month and then it showed in October. I’m thinking it might be the same case again. but before September I had a period every month, so I’m wondering what’s going on with my body to make me start missing periods every few months.