I seem to remember there being a sweet pea expert round here so I'm sure he'll offer you some good advice.
It seeems a bit too early for them to have done their bit, especially as how late everything is this year because of the weather. Take the pods off if you want the plants to continue to flower (you can leave a couple it you want to grow your own seeds for autumn/spring, as said above).
I'd give the plants a feed make sure they are kept well watered and take the yellow leaves off, you should then get a lot more flowers.