Moon jellyfish

At new Smyrna beach in Florida we saw many jellyfish washed up on beach... (Tuesday) went back to the beach on Thursday to swim... While swimming we started to feel a stinging sensation all over our skin... There were four of us... At first we each thought it was our imagination ... Then it got to the point we all had to get out of the water.... We all had the same symptoms... Not sure, but we're thinking there may have been many baby jellyfish in the water because we didn't see any, and occasionally felt something slimy float by our hands or legs...then had stinging all over....