Hi welcome to Health care magic forum.
Thanks for choosing H.C.M.F.
As you describe the period started 3 weeks back with pain all over the belly. Today morning you had pain in the lower tummy and back. It pains and remissions alternatively.
It appears to be pelvic inflamatory disease, If to the right could be appendicitis
, or urinary tract infection
. If to the left may be urinary tract infection. If near the navus may be due to intestinal worms.
I advise you to consult a gynacologist for diagnosis and treatment. You may need to have U.S.scaning besides other routine tests for confermation.
Wishing for a quick recovery.