What in my diet could be causing my ebf 3 1/2 month old to have painful gas that seems to be trapped? and if i take a probiotic would it help him?

Experiment: Different babies are sensitive to different things. Some may have a problem with cabbage, broccoli, dairy, nuts, etc. You should try to keep a diary of what you eat and try to relate it to when the baby gets irritable. Probiotics are not likely to help unless they are given to the baby (check with your pediatrician). Great job to be breatfeeding, you can work this out with some effort.

Probably nothing: Some people swear that their diet affects their breastfeeding newborn but studies have refuted that mother's diet does. So with good studies to back that up, your diet, nor a probiotic should matter. Some babies just have gas. You could try the gas drops in the pharmacy and see if it helps, or a peppermint drop under the tongue, but probably not much will help till he learns to work it out.