How to sing from diaphram? am i doing it wrong?

okay... well i know "how" it just doesnt seem to help, i breath in deep in my stomach and push a little...not to hard though so i dont over do it, but it still seems to hurt to sing.. even lip rolls hurt.. there is like a sharp pain lower in my throat.. I just got over whooping cough a little bit ago, and i have acid reflux and post nasal drip.. but i took medicine and stuff. but could those things be my problem?? yes i have gone to a doctor(ear,nose, and throat doctor), he did all these things to me and he didnt no why it still hurt...and it even sometimes hurts to talk...and hum...so any advice at all would help please, its been almost a year... anything at all would be nice.. thanks in advance for answer it means alot to me! :)