It sounds like you are not turning your hip over. You should be hitting with the front part of your shin, no matter what range you are at you should not be able to hit with your ankle. Do you have an instructor? Get one. Practicing Muay Thai without a coach is probably going to be a little fruitless.
As for that jab on the forehead thing, I don't think that that is true at all. I don't know about you, but if I'm in jabbing range I can hit my opponent with the top of my shin. The way I've always heard it explained, long range = kicks, medium range = punches, short range = elbows and knees. Also if you only kick in punching range, be prepared to take some shots to the face.