I feel small bubbles underneath my skin on my stomach and my stomach cramp a lot.

Need to examine: It is not feasible to provide an opinion about the "bubbles underneath the skin" without examining you. You may need to adjust your diet to address the cramps. Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine

Air under the skin: Is called subcutaneous emphysema. It means that air from the respiratory tract is somehow gotten under your skin. This means a defect somewhere. Usually when you press on it you can feel crackling and movement. If less you've had some other medical condition or injury this seems unlikely. But if you really do think it's air, it needs to be investigated by physician