I just started taking antibiotics and Prilosec for a stomach ulcer, how long does it take for the medicine to kick in start to feel better?

Varies. The length of time a patient may feel symptomatic improvement as a result of a treatment can vary from patient to patient. A patient should expect anywhere from a few days to a week to notice improvements. Speak with your doctor if you feel you are not improving. Cessation of smoking and alcohol can be beneficial to your condition. Take great care!