contrary to what you may hear from some reenactors, there were really no regulations in the Continental Army that disallowed beards. I've written an older answer about the US Army's changing grooming standards you may like to read.

But there are a couple of things we should bear in mind. Regulations like this aren't written in a vacuum, and for the Continental Army, most of these regulations were lifted word for word from British army regulations that many American officers would have been familiar with or had access to. They were also written with respect to fashion standards, which themselves would be a powerful influence on any man in the ranks. To make a long story short: if the army didn't write about beards, we shouldn't take that as evidence that they were tolerated, especially if the great weight of evidence tells us that beards were extremely rare among men in England and the colonies. If men shaved as a matter of their fashion customs, they wouldn't stop when they were in the army, or if they mustered for militia duty.

If you've taken a close look and found some men wearing beards, and it sounds like that's only a very few, you might want to take the greater weight of evidence to suggest that it was, in fact, quite unusual to see a man wearing a beard while in uniform for service. Precisely because it was rare to see a man wearing a beard at all, because that was fashionable at the time. This is a pretty settled question. Even reenactment blogs and websites cover it pretty closely and with great detail - take for example this post, specifically about British sailors, finding examples of men with beards in period images that are all specific images of men in specific circumstances that are meant to be taken as unusual and pitiable.

Dr. Alan Withey has also written of this topic somewhat regularly on his blog, which might be worth a look.