Thanks for the query.
Menstrual cycle length and time of ovulation varies from person to person and can vary in same person also.
Usually cycle length between 21 to 35 days can be taken as normal.
Weight changes can affect the menstrual cycle and also the time of ovulation.
And urine pregnancy
test kit may not detect early pregnancy sometimes.
So, better to go for blood test
for pregnancy or ultrasound
Compared with urine test for pregnancy, above investigations usually give accurate result.
If they exclude the possibility of pregnancy, possibly you will get periods soon.
Decreasing the weight can help in regularization of menstrual cycles.