Hello,
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After tubal ligation pregnancy chances are possible but since it has been about 3 months by now the pregnancy test would give up results.There could be various reasons of the above reported symptoms as hormonal imbalance due to any underlying uterine abnormality as fibroids,endometritis,thyroid hormone abnormalities or even ectopic pregnanc which is a possibility after tubal.
You need a careful pelvic examination and investigations as USG scan and Blood test which would help in ruling out the cause so that accordingly treatment can be started.
Kindly visit a Gynaecologist for evaluation.
Take care!