I put my sweet peas in the ground some time in June. They started blooming about 3 weeks ago and are still going strong. I have never tried to grow them in a pot. I wouldn't give up on them yet if I were you.
Bonny

Mine started blooming about two weeks ago. They still aren't very big. I think you'd be safe to wait a few more weeks for them.

Haven't been on for a few days...thanks for your replies. I planted out my sweet peas on June 1. I have grown them in a pot before because I never got more than two plants, and even in a small pot they grew and I got one or two blooms. However, over the past few days, I removed the calendula from the pots and realize that several of the plants were yellowing from the roots up and I could not see that. Perhaps having the calendula in the same pot was too much. So I have topped up the pot with compost, gave it a good feeding and will hope for the best.