Your problem seems to be oral submucous fibrosis which is reduced mouth opening mainly due to gutkha chewing. It can be corrected up to some extent by taking medicines, injection and performing jaw exercises on daily basis. Fastest treatment is by laser
surgical removal of cheek fibers. So you see its not one day job to correct your problem unless surgically treated. Also you must quit the habit completely by the time you go for treatments else it will fail.