Yeah, you can still train, just dont do anything that causes you to "strain". The belt is also likely a contributor, alot of people wear belts too tight, especially when starting to use one for the first time. It doesnt need to to be extremely tight, you just need to be able to push your stomach into it, its there to give u something to push against not to squeeze the life out of you. That issue youre dealing with is very common, especially when people start to use heavier weights and strain more frequently.