I experienced mild dizziness a couple of times in the weeks after starting Dapagliflozin, though no muscle soreness. At the time I read up on it and read that many of the side effects are actually related to dehydration, caused by the flozin's effects in expelling glucose via the kidneys into the urine. Muscle soreness is a potential symptom of dehydration, so it might possibly be that. I still feel a little spaced out sometimes, though I put that down to my weight-loss diet, not the flozin. It feels like I've slept too long - a low energy feeling, not 'firing on all cylinders' - and I've assumed that was just lowish blood glucose levels - a combination of the meds and my diet.
This list of potential side effects includes feeling faint, lightheaded or dizzy, though not thigh muscle pain specifically.
www.mayoclinic.org
Be sure to drink plenty of water as that may help to prevent side effects including the most common one - UTIs. The few short dizzy spells did pass after a couple of weeks.