full squat anterior leg pain?

Hello

I'm wondering if anyone can help me.

When I first started foundations, I couldnt squat down all the way while keeping my heels on the floor.

 Ive eventually gotten to squatting down all the way, however slightly have to keep pushing myself forward to prevent rolling backwards, but I noticed now that I can get that low, my anterior leg, the front and slightly lateral part of my shin muscle starts to burn. 

Why is this? How can I prevent this flare up? 
If I try to do pistol squat as well, for example, it hurts kinda like its on fire

Thanks in advance!

Hi Monica,

Sorry to hear about this pain! It sounds very uncomfortable. Have you consulted a doctor about this? That is my best recommendation for you if you haven't. @Alessandro Mainente may have some more insight for you. 

It is a normal nervous reflex, but moving the weight forward you are forcing the dorsi-flexion of the ankle. since you have tight Achilles tendon the body reacts by squeezing the tibialis in order to stretch more the posterior chain.