after 5 months i had a 6 week period, which my doctor wasnt too concerned about (so long as it doesnt happen again), it really depends on how the bleeding is - for me it was quite light so i wasnt loosing much. if youre heavy etc id suggest seeing a doctor about it.
the way it was explained to me was that because i wasnt ovulating my body had stopped shedding as normal but was still creating some of the normal lining which grows at the beginning of your cycle in preparation for ovulation. i hadnt had a period for a few months, so my 6week period was likely just a build up of lots of old tissue.
see how it goes, if it goes on any longer id suggest seeing a doctor, its better to be safe than sorry, but i really dont think its anything to worry about.