Welcome to HCM.
You have missed period over a month.So first have to exclude pregnancy
by urine and blood HCG test.
If test is negative,then have to search for other reasons.
There are several reason of missed /delayed period with cramp/low back pain
. They are more like with Oligomenorrhoea as in PCOS, Thyroid disorder
, heavy weight,psychological upset, abnormal eating habit etc.
It is better to do a fresh USG lower abdomen to rule out underlying pathology.Along with you can do other tests like Thyroid profile, PPBS, LH/FSH, Blood prolactin
and lipid profile
Always consult with your doctor regarding your test results.
Also you control body wt, take healthy diet, avoid emotional or stress full activity and take proper sleep.