very sore upper arms

[gaorii]

Hi! I'm new here and pretty new to knitting. I find that if I knit for any length of time over a day or 2 I start to get really sore upper arms.Does this happen to anyone else, and if so, what am I to do? any suggestions? I had to quit knitting last year for months, but found I really wanted to do some things for my niece who is preggers. Now, back to the sore arms...

Second questions, I assume all the patterns here are using US sizing for needles? It would be helpful for non-US'ers to say that it is US when typing the patterns, and we can convert to mm's or British/Canadian. I have so many old needles from my mom, all in different size systems! boy!

Gaye