hmm okay, the stiffness of your muscles is most likely a side effect from the benztropine.
do you stop taking the clonazepam at all? if you stop a dosage suddenly, it can lead to stiff muscles. seroquel also has similar side effects. in the meantime, try using warm compresses where it gets stiff. deep breathing exercises may help you also, inhale through your nose and exhale through your mouth.
either way, swelling of the tongue doesn't sound good. does it inhibit your ability to swallow? if it does, see a doctor ASAP because it can increase your risk of not being able to breathe properly. even if it doesn't inhibit your swallowing, go see a doctor just for the peace of mind. better safe than sorry