I Water in the morning round the base and not on the leaves. sounds like a mildew/fungus perhaps from the wet weather we have had?
The other thing that comes to mind re lack of flowers could you have over fed them?

I thought the same as you last week, but a few days sun and suddenly I'm picking sweet peas.

8 is good. I've only had 4 so far!

http://www.lathyrus.com/culture/path.htm

That gives a list of most sweet pea diseases. Check the growing point...if that looks stunted then it's a virus.
Mottled leaves can also be a sign of aphids.
Never known overfeeding to cause lack of flowers though.

It has generally been a bad year for sweet peas for a number of reasons, mainly bud drop in my case.
At the national show last Saturday at Wem, entries were well down. I managed to cut 28 stems from 130 plants.
However, as has been said, this sunshine has worked wonders so persevere. Yesterday, I cut over 100 stems, all far better than what I entered at the show.

If you do feed, high potash such as a tomato feed is better, as nitrogen feeds encourage too much top growth and few flowers.

Never used it myself but in order to keep the length of stem going, a top dressing of dried blood is recommended about a month after they start flowering....which is pure Nitrogen. May give it a go next year just to see what happens, just before I layer them.
Chempak no8....low nitrogen, high potassium is one I have used.

Thanks everyone, lots of helpful advise and information here! :)