Iphone freeze?????

I just got my iphone 1 month ago.....I have been facing this problem....The pictures like games/videos are still moving/working in the screen...but no matter how i touch the phone screen, it dont detect my touch....but if i shake it slightly it will be able to detect again...and happen often...so I did try the on/off and home button thing.....but it hang at the apple screen quite long then it back to the main screen....and sometime when at the slide to unlock ..it will also freeze there and i totally cant do anything....have to keep pressing the home or on/off button....still thinking should i go for exchange ....Anyone know what to do...thanks in advance