My phone keeps losing signal when using Wifi or 3G

So Ive had a bit of a hunt around but cant seem to find anyone who has this exact problem.

I have a iPhone 3GS, and have had no problems with it whatsoever. However, recently whenever I am using an ap that is sending/receiving data (either through Wifi or 3G connection) my signal drops out every minute or so for several seconds, before searching and reconnecting, and resets my Wifi connection also. However, when simply texting or talking on the phone this doesnt occur. The problem seemed to have begun after installing iOS5, but since updating to iOS5.1, it still remains the same.

I have tried all the basics of reinserting my sim, restarting the unit, as well as trying a soft reset etc. It seems odd that the problem only primarily occurs with 3rd party aps, such as banking, chat and social networking including facebook.

Help?!