The county ext service advised me to be sure and rotate crops. I advised her that would be difficult since it is only 11’ x 16’ She said only a couple of feet would be enough, and went into a trance rattling about nematodes and such. Well I took her advice, they are the experts, we plant maters on one side of the patch then the other side next year. The unused part is where we experiment around with other veggies. Last year we tried watermelons and cantaloups: they grew and grew, but never any fruit.
Its all fun.
I wonder if your soil may be too acidic?
Culture
Melons like full sun, hot days, warm nights, and lots of room to grow. They also need moderately rich and well-drained soil that has a pH of 6.0 to 6.8.
Melons really dislike extremely acidic soil, so choose a spot that has naturally alkaline soil, or has recently been limed.
http://www.weekendgardener.net/fruit/melons-070807.htm
Heat may also be an issue:
http://bonnieplants.com/growing/growing-watermelons/