You are suffering from Irregular delayed period for last few months with body ache.
There are several reasons of delayed period besides pregnancy
.You also get negative test.
Other causes are Ovarian Cyst/PCOD,hormonal imbalance,over wt/extreme loss,stress,emotional upset,eating disorder
,thyroid problem etc.
So do a USG lower abdomen,LH/FSH,Thyroid profile,Blood estrogen & Progesterone
to rule out underlying pathology.
Then consult with your gynecologist and take advice according to test reports.
Control body wt by regular exercise,avoid stress,take healthy diet and sleep properly. You may take some anti spasmodic medication like Tab DROTIN DS or Muscle relaxant
gel for LBP.