Anti-histamine and BG

I've been taking Piriton (which I believe is an anti-histamine) as got bitten by insect unknown on legs, body & arms. One of these swelled up to about 1" diameter. There was no sign of infection when checked by nurse. This also occurred in 2013, first summer since moving to current house. I used to get bitten, mainly around the ankles but no swelling.

My BG levels sometimes seem to rise (up to 12-14 range) for a while when taking Piriton and treating the bites with a cream.

I was wondering if any others have similar issues with Piriton or similar medications?