This is a good question. You need to see your doctor
as soon as possible to have a full history and be examined and make sure that there is not something else going on besides your yeast infection. It is possible that you were misdiagnosed and there is another cause for your symptoms, such as an STD
(sexually transmitted disease), so you need to be tested if you are sexually active. Herpes can cause a lot of swelling and pain but usually also has blisters and ulcers, so if the rash that you are describing looks at all like this you need to be tested for HSV (herpes simplex virus). It is also possible that you are having an allergic reaction to the medication if your doctor prescribed your medication in a topical form (a cream, lotion, gel, etc). This could cause swelling and a rash. The other possibility is that you did have a yeast infection along with something else, such as an STD. Again, it is very important for you to see your primary care doctor
or gynecologist right away to have a full exam and possibly testing to determine the correct cause of your symptoms and to obtain appropriate treatment.