When your down and blue over all those rejection letters remember some of the more famous books that were passed up many times by otherwise savvy agents and editors. Keep in mind that this is a very short list of authors and their books.
Zen and the Art of Motorcycle Maintenance, by Robert M. Pirsig, was rejected 121 time. The book went on to sell over three million copies.
A Time to Kill, by John Grisham's first book.
Clan of the Cave Bear, by Jean M. Auel's first book.
The Spy Who Came in from the Cold, by John Le Carre'
The First Wives Club, by Olivia Goldsmith
Keep writing. Never give up. Keep your spirits high.