Sudafed and low milk supply

Laura • My partner and I are expecting our first together in January :-)
My son was born exactly one week ago and my milk came in after a few days, however I have had a low milk supply and have to supplement with formula for him to gain weight. I was sick before and after he was born and was taking sudafed. I just read online that sudafed can cause a low milk supply! Has anyone had experience with this?