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There are some menstrual abnormalities known to occur after using Copper-T. You can wait for 2-3 more cycles which should be normal by then, if not you can get examined by your Gynaecologist who will rule out any obstruction or uterine problems. Regarding the weight gain, if it is sudden it could warn of an ovarian cyst
for which you should get an ultrasound
as well. Eat healthy, fresh green vegetables, plenty of water, exercise by brisk walking for 40 minutes everyday. This will help to reduce weight.