Could a grade 1 sprain if the thumb joint last for 7 weeks? or could my injury be more serious?

More serious: A grade one sprain at your age should be mostly healed. If you are using it a lot or re injury the hand it could delay healing.

See your PCP: for evaluation, imaging and referral. 7 weeks is too long. If this ligament injury is not diagnosed and treated properly, it may lead to chronic instability, weakness, and ultimately arthritis and more unnecessary aggravations.