Burning Mouth Syndrome Or Something Else?

One day last November I awoke with a 'bitter' taste in my mouth.

Several visits to my GP later and I'm still not much further forward.

I'm a 43 year old female. In October 2013 I was diagnosed hypothyroid and began treatment of 50mg levothyroxine per day. Because the bitter taste started relatively soon after beginning the medication, I put 2 and 2 together and thought it was causing the taste. But, no, I took myself off the medication for 3/4 weeks over Christmas and still had the bitter taste.

I've drastically altered my diet as I thought certain foods made it worse but can't pinpoint one particular allergy or sensitivity.......

I've changed toothpaste, tried mouthwash, cut out tea, milk, all dairy, and mainly eat very healthily - fruit, veggies and chicken.

My GP suggested LPR (silent acid reflux) but it doesn't taste like 'acid' - it's just bitter/sour.

I've been on Gaviscon after every meal for over a month and Ranitidine for almost 2 weeks. The symptoms persist still

My mouth can get quite dry, and the bitter taste seems to be on my tongue and/or the roof of my mouth or around a wisdom tooth on one side.

I can't cope with this for much longer. It only eases up when either sleeping or eating.