Ewes should only need to be wormed at lambing beacuse adult sheep have some resistance to worms, but at lambing when the ewe is under stress, she excretes lots of worm eggs which in turn infact the new lambs that have no immunity.
Lambs will probably need wormed over the summer but it depends on your stocking rate, what's been on the land before. You could do a faecal worm egg count FEC and worm if you need to - your vet will provide a kit for small cost and will give you advice based on the outcome of the test.
Your vet will also advise of flukicide. We do the ewes at lambing, tupping and scanning. We only do this seasons lambs if the weather warrants it - like it's been bone dry here so far, so we probably won't have to fluke the lambs this year.
You would be advised to use some sort of fly strike preventative - there are ots on the market - Crovect, Clik. NOAH - National Office of Annimal Health has a good compendium where you can look up vet meds.
The website SCOPS has good advice on use of wormers.
I assume you're done the lambs with Heptavac or similar?