No period but not pregnant

I feel dumb even posting this because I’m a 28 year old mother of 3. I feel like I shouldn’t be stressing over this BUT

Since I had my first period at age 9.5, I have NEVER skipped a period or been late UNLESS I was pregnant.

I’m now 8 days late and have been cramping the entire time. I am not pregnant. My husband has a vasectomy 5 years ago and I also took a test just in case because I know it’s rare but it can happen. Test was 100% negative at the 5 days late mark.

I wouldn’t be worried if it weren’t for the face they this has never happened to me. Should I be worried about my health?