RP: Starting solids and rash Q

MrsG2B07

I'm any response from 6-12 so maybe someone here can help me.

Okay...long story short we started oatmeal and rice cereal over 2 weeks ago.  She didn't poop for 4-5 days and when she did she broke out in a red rash all over her diaper area that over the following days spread to her thighs and belly and eventually almost covered her body.  Took her to pedi and he said he doubted it was from the food, more likely a viral infection from a cold she had. 

So, he said keep going with the solids so 3 days ago we started bananas.  She just pooped and as soon as I took off the diaper (she was in it for maybe 3-5 minutes) her bottom was bright red and the same red rash is now spreading to her belly and thighs.  

So, is this normal with first poops from new foods or is it an allergy?? Or could it be from the viral infection?  Anyone else have experience with this?