Weight gain, bloating
are common consequences of quitting smoking
. Tobacco lowers your appetite and increases the motility of the gut. So when you quit after years of smoking, there is increase in appetite and reduction in gut motility, leading to weight gain, constipation and bloating due to gaseous distension, which makes your belly feel like a balloon, as you mentioned. It usually improves with time, but the time required is variable, depending on many factors like how long and how much have you smoked, how good was your digestive system when you started smoking, your lifestyle etc. The solution is not restarting smoking, but to improve your lifestyle. It is good that you take regular exercise. You can also benefit by taking small frequent meals, rather than two or three heavy meals. Also add fibre to your diet. If possible, take up yoga
Hope to have been of some help. Best wishes.