Both my big toes have a burning sensation under the nail beds. they are cracking and bout to fall off! no thyroid problems and don't think its fungus!

Toenails: Your medical history is complicated. The problem with your toenails has many possible causes have them evaluated by a dermatologist. It could be due to an infectious (bacterial or fungal) , or immunologic, or physical etiology. The burning may or may not be related to the cracking of your nails.

Yes: See your podiatrist to have a fungal culture done of the toenail.