I started off on violin and am now primarily a violist for string instruments, and recently I rented a Cello as well. I'd like to play Cello pretty proficiently, but for some reason it seems to be painful after more than just 15 or so minutes of playing. My bow arm gets really stiff. Is there anyone out there who plays Cello? Is this just normal when starting out on Cello or is there probably something wrong with the way I'm holding the bow?