If i try and sleep without sucking my thumb, i clench and grind my teeth and wake up with head and jaw aches. do i need a brace/retainer?

Yes: You need a jaw protector. Probably you should talk to your dentist or pharmacist for one. Very simple in design and you put it in at night and your jaw can clench but no harm to teeth an should give you releif from muscle aches. If you can afford to see your dentist he will be able to custom fit the bite pad you get.

See a dentist: You've developed a TMJ problem that will worsen over time. Do not try to manage this with home or store bought remedies. They are unpredictable and can cause damage. A bite appliance that helps you position your jaw in a relaxed position can eliminate the grinding. You also may have sleep apnea.

Bite help: There are various dental appliances to correct this problem. You shoiudl not continue to treat it with your thumb.

Evaluation: This is not a diy project. You need professional help. Is your clenching/grinding due to malocclusion, stress, emotional issues, jaw malrelationship, etc? Otc gadgets can do more harm than good. Occlusal orthotic may relieve symptoms but not fix what's wrong. Start w your dentist. He may rx you or refer you to orthodontist, oral surgeon, psychiatrist, neurologist, etc.