Tomato problem

I have a raised garden and always plant about 8 tomato plants (two of each variety) always with good results. This year I put in 8 plants (4 varieties). We had a lot of rain. Two plants died when covered with green tomatoes and the rest all had huge, distorted tomatoes on them. They all looked like about four or five tomatoes grew together from one stem. Anybody know what causes this problem. I like the idea of two pound tomatoes but these were horribly shaped. TIA Allan