Hello,
Thanks for posting on HCM,
If both blood and urine tests show negative, then it is very likely that your lateness is due to another cause other than
pregnancy. I recommend you do a pelvic scan, just in case, both lab tests were false.
If you are having
gastroenteritis, it may mean that you maybe suffering from some sort of infection which could be coming directly from your gut or maybe from another affected system such as your
urinary tract, pelvis organs etc. I will normally would have ran some tests such as CBC, ESR, CRP,
urinalysis,
widal test, stool exams etc to find out any loci of infection. An infection could have induced absence of menses (through stress mechanism).
So if pregnancy is completely ruled out, you will have to be patient for menses to start again or your doctor may prescribe a drug to induce period and regulate it.
Hope this helps