I travelled to america for 1 week at easter time and I am now planning to travel around america for 3 months in september. Will I have a problem getting into America as I have alreday been once this year? Many Thanks
3 months is (just) more than the 90 days which is the maximum you are allowed in for on the visa waiver scheme. You might have to trim things by a day or two.
Your visit at Easter should have no bearing on it at all - you've been back home (I assume in the UK) for long enough for your September trip to be regarded as new and nor a continuation of the Easter one.