my muscles in my upper arm are tensing upeven though i use my wrist ....why is this and what shud i do when am picking?

That's happening because your playing is too tense.

Try not to make your picking too sharp and deliberate, it should be smooth and relaxed (whilst still maintaining the sound you want).

It's quite hard to always play relaxed but it's important, you might end up with RSI which would just stop you from playing for ages.