It could be your stem length. A shorter stem should bring your body more upright, shifting weight off your arms. Is your seat pushed way forward or back? To start off with, it should be centered so that there is an equal amount of seat rail showing ahead of and behind the seat post clamp.
The shop you bought the bike from should be happy to help you with this. A good shop will also swap your stem out for a shorter one of similar value, for no charge.