Disappointing nappies

My daughter is 8 months old and she uses pampers since birth. The very first pack used was fine, the second pack made her get a very bad rash. I've stuck to pampers and she was fine again till she started using size 4+. She has a very bad rash that keeps getting worse. If the nappy doesn't leak the my daughter gets a very bad nappy rash. I am done with Pampers, I bought them in bulk and now this happens.