Quit habits strictly. Seems like you have oral submucous fibrosis (OSMF). Kindly consult an oral & maxillo facial surgeon in person for further suggestion. We need more investigations with clinical examination to decide upon treatment. You may need conservative or surgical management for mouth opening depending upon the stage of OSMF .Advise full mouth opening, ballooning
exercise & side to side movement of the jaw. Wrap 25 to 30 ice-cream sticks, make a bundle, put it between upper & lower front teeth for 15 minutes thrice a day increase 1 sticks each day.