Twitching thumb

[Eruss]

Have had this for a few weeks now on and off, not my dominant hand but one I use to text or scroll on phone.
Tried not using it as much but no improvement .
Any ideas or advice?

I've got this too. Do you twitch elsewhere? Might be benign fasciculation syndrome. Twitches by themselves are unlikely to be anything serious.

No don’t twitch anywhere else apart from my eyelid once in a blue moon if I’m really tired

If you have regular eyelid twitching then it's most likely b12 deficiency, if it is just your thumb then it is caused by overuse of phone.
I had the same issue few days ago and tried the exercises as below.
www.healthline.com/health/de-quervains-tenosynovitis-exercises#opposition-stretch
Also used some pain relieving gel. Avoid washing your hands with cold water.