My best diaper rash trick is to use a hair dryer to ensure the skin is COMPLETELY dry before applying any cream. I used very little diaper cream while my daughter was in diapers because I made sure she was dry when changing her...rashes (including yeast infections) cleared up in a day when I had to use a cream. I like Aquaphor, butt paste, and Wedela Calendula cream for rashes.
One thing, ask your doctor for the correct dose of Tylenol and Motrin. If you are going to administer pain and fever relievers, you should give them in the FULL correct dose. Otherwise you are just giving them something for no reason AND if it doesn't work, it makes it too easy to overdose them when you try to give them more. I'm not scolding you, I used to think that less was more too...I hate giving my daughter anything, but my doctor explained why it doesn't make sense to give less than the recommended dose for weight.
I second the Hyland's tablets...worked great for my daughter.
Nothing you describe sounds too concerning, but you do need to get the rash under control or it can get infected. Try rinsing him in clear water several times a days to really get everything off his skin. Adding a little baking soda can take away the sting. Dry throroughly before diapering.