Hey and welcome gododdin,

You will be much more aware this time around since you have already had the problem. I have worked with quite a few professionals that have had problems caused by unnecessary tensions while playing. As Daniel mentioned above, you need to find equipment that allows you to hold comfortably without the need to grip. I have found that people with chin-rests that go over the tail-piece have less trouble with shoulder pain than the ones to the side. Also, even though it is called a chin-rest, it is usually used as a jaw bone rest.

A lot of people loose the perspective of where their tensions are being used when concentrating on playing. You need to keep this in mind in every session unlike what you were probably doing the first time you played the violin.

Look at my videos on how to hold the violin, since you were self taught, and try to balance the violin instead of holding it so hard. The only time I really need to hold the violin is during a downward shift or when playing very acrobatical music like Paganini and such, and then I try to only hold it and not grip too hard.

If a note is hard to reach see if moving your arm to a better position allows you to play with less tension. Experiment this time to find the most comfortable positions and holds and remember you are starting over again. Start slowly and carefully.

I used to take my summer vacations from the orchestra and after not having played anything for 6 weeks I would take out Bach and Paganini to get back in shape thinking I could play as long and as hard as ever but would always feel it the day after.

Good luck and I am fairly certain you can do it without much pain, and that the pain will be temporary as with many physical activities and sports. Once you get used to playing you should be ok providing you have paid close attention to proper technique and relaxation.