How have they diagnosed it? Did they just do an ultrasound? There is a guideline about how thick the lining of your womb should be - from memory I think it goes from 3mm-12mm depending on the stage of your cycle. Mine was at the upper limit just after a period when it should be at its thinnest, so although within limits, it was felt to be sufficiently abnormal to warrant investigation.
Mine was also felt to be hormone imbalance (due to PCOS) but as a short dose of the pill didn't stop the erratic bleeding, the gynae moved on to the scan and when that measured thick I had a D&C and biopsy which was thankfully clear.
At that point she advised me to have a mirena coil fitted to keep my endometrium thin.
I would think your best bet is to persuade your GP to refer you to a gynae and discuss your concerns with them.