Excessive clenching of your teeth will lead to severe attrition of your teeth . The muscles of your oral apparatus will get fatigue. Temporomandibular joint disorders and trauma from occlusion takes place as long term effect of clenching. This will further lead to painful mouth opening as well as reduced mouth opening.
Next Steps
first thing you should do is try to break the habit yourself.
after that go to the dentist and get the cause diagnosed.
nightguards can be fabricated for you . and if there is some trauma to TMJ then that also can be taken care of.