Hi, Welcome to Health care magic forum.
You are telling that your boy friend had vasectomy
,means you can't become pregnant, unless it is failed.
Your late periods, in spite of your regular periods, the cause may be the anemia
, or infection, and the pain also suggests the infection.
You can have a home pregnancy
test, to exclude the pregnancy. If it is negative i advise you to consult a gynecologist for diagnosis.
Take more of green leafy vegetables, pulses, sprouts,and
protein rich foods to have a good health.
Wishing for a quick and complete recovery. Thank you.