This can be de Quervain's Tenosynovitis. It is inflammation of tendon sheath of the tendons of the thumb. You should consult an orthopedic specialist or specialist in physical medicine and rehabilitation. The treatment is following;
1) Thumb and wrist splint
2) Deep electrotherapy done at physical therapy (iontophoresis / phonophoresis).
3) Physical therapy
4) Steroid shots
5) Anti-inflammatory analgesics.
Please read about it in this resource:
Since pain is excruciating, it is advised to go to urgent care or ER for an injectable analgesics.
Ice compresses can also help you.
Keep it raised as much as possible.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.
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