My baby's first diaper rash

Sky08

I noticed Friday that my son's rear end was a little red.  He also screamed when I went to clean him with diaper wipes.  Today it is really red and is very chapped.  I have been putting vaseline and desitin on him, but it seems like the red is getting worse.  He is almost three weeks old and I saw on the internet that if your baby has a diaper rash before six weeks that you should call your physician.  His formula got changed and I have been using pampers, but I ran out.  So I used huggies that my friend got me.  I didn't start noticing the red until I was using the huggies.  So I think he may be allergic to the huggies, so I switched back to the pampers.  It breaks my heart to change his diaper everytime I have to change his diaper.  I have tried to keep it dry down in that area, but it has been tough because it is like I am constant watch to make sure he doesn't have dirty diapers and I don't want his rash to get worse.  I am not sure what else to do.  I just dread changing my son's diaper because he cries and screams so much and it bothers me when he cries.  I am sure it is because I am going through baby blues right now.  Does anyone have any suggestions for me?  Is anyone going through this right now?