Quick question - been playing for five years, very use to hard skin on the left-hand finger tips, but now have a build-up on the right-hand thumb where it seats under the bow hold. Is this to be expected? I have increased practice over the past few months and the grade piece I'm working on has a lot of bow crossing, which means I'm lifting the bow more than I'm use to. Any guidance and/or reassurance would be much appreciated. Thanks, S

I have a kind of inside lump on my thumb between nail bed and joint - looks like an extra piece of cartilage but it isn't! Plus a calloused dent in my 1st finger where it leans sometimes on the bow wood as the leather cushioning isn't long enough, and of course, the left fingertip hard skin! All musical war wounds, as it sounds like yours is.
You could always go to the doctor for re-assurance. I have the neck 'hickey', but recently have noticed a hard lump inside under it. I am assuming for now it's all part of the same, but if it gets bigger I may also just check with the doc