Definitely go back to the LBS, or another one, that can fit you on your new bike properly! Also, it is not uncommon for MTB-ers to have hand problems when they switch to road. Check that seat position to make sure you are not tilted down and sliding forward in a way that puts pressure on your hands. Loosen the death grip on the bars. And, most importantly, change your had positions frequently! Try alternating between draping your hand over the brake hoods (thumb on one side, fingers on the other) and gripping the flat part of the bars closer in towards the stem. Remove one hand from the bars at a time and shake out, flex fingers a few times, etc and do this frequently. Good luck and happy riding