Hi this is quite common and the alloy wheel and hub corroded together and make the wheel hard to get off. I tend to put one wheel nut back on but only a few turns and then using a rubber mallet hit the wheel rim from behind rotating the wheel each time. Once the wheel is off I would recommend that you clean up the surface where the hub and wheel meet espacially where the hub sticks out as that is where they stick. Then apply some copper grease to the hub surface before refitting the wheel.
I hope this helps and if I can help further please feel free to ask.