My doctor says i'm allergic to dust mite (f) but not (p). what's the difference? what do the p and f mean?

Subtle Difference: Der p1 (Dermatophagoides pteronyssinus) and Der f1 (Dermatophagoides farinae) are the two major mite allergens. If you are allergic to one and not the other it doesn't make much difference. Basically you have a sensitivity to dust mite and should practice avoidance measures: dust mite covers to mattress and pillows, wash sheets on hot cycle once weekly, remove upholstered items from bedroom, etc.