Dot - Piriton tablet side-effects from their website - you're lucky you've only got the rash!
Occasionally some people may have difficulty concentrating; blurred vision; loss of appetite, indigestion or upset stomach, feeling or being sick; diarrhoea, tummy pain; liver inflammation (which may make you feel weak, sick and turn yellow); difficulty in passing water; headaches; dry mouth; dizziness, palpitations (feeling your heart beat), fast or irregular heart beat, low blood pressure (you may feel faint), chest tightness; thickening of phlegm; blood disorders (anaemia); allergic reactions including itchy rash, skin peeling, and sensitivity to the sun; twitching, muscular weakness and inco-ordination; ringing in the ears; depression (low mood); irritability or nightmares; children may become excited and the elderly may become very confused.