I have encountered this before where my period will miss for 2 or 3 months. Then the period will come and lasts for 2-3 weeks.I have seen a doctor and prescribed hormone treatment. After that my period comes ontime however i put on massive weight and now my period lasts more than the 7 days and there's a lot of blood clot , big jelly like pieces and it's really annoying. I don't lethargic though during my period. Just hate the sensation when the blood clot is coming out.