Mouth sores

My daughter (9 mos) was sick a few weeks ago and had a high fever. I took her to the Ped and they said to keep her fever under control and go home, rest, fluid, etc. Then last week, she gets hoarse and had a low-grade fever. Now, she has mouth sores. I took her to the Ped again yesterday. They said it wasn't strep. Her hoarseness is almost gone. She is teething like a muther effer also. They thought it was hand-foot-mouth disease, but the ped looked at her body and said it wasn't that. Push fluids, rest, and return to daycare. Now she has a diaper rash. I'm so frustrated. Does this have anything to do with teething? Should I get a 2nd opinion. Is one thing related to the other?