hi! we've dealt with diaper rashes EXTENSIVELY for 2 years; the yeast rashes, the non-yeast, the bloody, etc etc. usually after a round of antibiotics, it is the 'yeast rash' which has red bumps. the only thing we've found that helps is called vusion, a prescription cream...i hope you have prescription insurance, though, b/c it's still $30 even with our very good insurance coverage. but, our pediatrician had samples! (we have gone through about 10 tubes of vusion over the past year, when we first used vusion...we now just have a standing refill b/c our daughter gets diaper rashes so often). vusion is applied only 3 times a day & topped with desitin & then the ORIGINAL desitin (not the 'creamy' version) is used with all other diaper changes (that should be applied "like cream cheese on a bagel" as a ped. has once suggested to us).
if it's not a yeast rash, what we've found that works is what our former ped (from boise, idaho where we used to live) is called "butt paste" which is a mixture of same parts (we used 2 oz. each) (original) desitin, hydro cortisone cream, antibiotic ointment, & vusion (or another prescription yeast cream). just mix it up in a plastic container (we found a knife works best) until thoroughly mixed; it is applied every diaper change.
we also have tried mixing a dye free/scent free antacid (such as malox) with desitin which helps reduce the acidity of either the urine or stools.
also...do 'diaper off time', which is very messy (urine is usually everywhere) & when our daughter was that age we just put her on the changing table & kept her entertained for up to an hour. we do this several times a day. the air is really the best thing for rashes, especially the yeast rashes (b/c yeast grows in wet, dark places, like diapers...) so the more fresh air & light that you let in, the faster the rash will go away. be prepared with lots of either cloth diapers to put under the bottom (or towels). this gets more difficult the more mobile the child is (esp a 2 year old who refuses to be potty trained!).
i hope this helps! we really battle diaper rashes at least twice a month, so if you have more questions, please email me, i'm very well versed in these rashes ;o). really, you will most likely have to make a trip to the pediatrician to get a prescription. after antibiotics & a stubborn rash, prescription paste is really the only thing we've found that helps.