My fingers go numb if i play trills or double-stops for quite a period of time.
But my exam is just round the corner, in early December

I dare not take days off practice because I scared that my playing will deteriorate during my break, and I need time to build up my scales, arpeggios, again. Just realize, I might be pressing on the strings too hard! My finger cuts heals after 2 days not practising, but it is more severe, I need up to 5 days for it to cure.
I take about 3 short breaks between my practice each time (about 2 hours). And about keeping fingers 'anchored to the neck', my teacher told me to do so when I asked him about the scales. Well, I am only going for lessons 2 weeks before my exam. Guess I have to sort things out then. Hope it is not too late! I am now 'teaching' myself
But i think my playing posture should be correct, since I didn't get any back pain after playing for 2 hours standing. I don't get wrist pain from playing my pieces, just finger pain after playing Gigue from Bach's partita no.2 in D minor, which is supposed to be played very fast.

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for my left hand it's the wrist which feels twisted and the lower arm which also feels twisted
Exactly! That's what I feel like! I am using 4/4 size violin but I am in my twenties already...
Thanks for your replies...I will 'try' to reduce my practice...