pimple nappy rash

[june79]

My baby is 8 weeks old and he has got a stubborn pimple near his anus. The doc changed his cream twice but instead of going away, there is another one coming up. I change his nappy right away after he poops. He was on Huggies and changed to Pampers. Changed cream from Sudocrem to Metanium and is on Clotrimazole cream. But nothing seems to work:(
How does the pimple dry up? Does the pus comes out and then dries or it just dries off?
Secondly, do you think it's a good idea to put him on antibiotics to treat the pimple?

Any suggestions are very welcome.
It hurts to see him with such big pimple getting worse every day.