I have been using medicine for ringworm for three days can i go swimming?

Yes: I assume you are using a topical antifungal for the ringworm (a fungal infection of the skin and not actually a worm despite the name). If you are using a topical treatment and are swimming right after you normally apply the medication, wait until after swimming and then apply to avoid it being washed off before it has penetrated the skin. If it is a pill, swimming will have no effect.