Morning Danny
You're obviously having some sort of reaction to the Piriton, so i would either go back to your doctor/call him/her for advice so you can be prescibed something else that wont , hopefully affect you the way the Piriton seems to be.
Your chemist may know of something else you can try, but may be best to check with your GP first.
We're abroad at the moment and some of our families/groups are using it against insect bites/stings, and no real ill feeling, so could be you are allergic to something in the pill.
Having said that, some medication do have a slight reaction in some people, as they advise of this on the instructions.
I'm sure you will get some good advice on here from great posters such as Sqad etc later, if hopefully they see it, so good luck and all the best to you.
cheers
yogi