HELP, I Have To Sniff My Girlfriend’s Undies To Get Sexually Aroused

“I’m a 29 years old man, dating a 24 years old girl. I am sexually active, and have a great sexual life with my girlfriend. The problem is that before i can get aroused, I have to sniff my girlfriend’s used undies (panties to be precise). I really do love the odour, it smells like sweat and vinegar and that is what turns me on. She doesn’t have a problem with it, but people think this is weird and abnormal and I’m just scared because  I might contact some unknown kind of disease.

Do you think this normal? Am I alright? Please help me out”