We have just introduced solids to our 6 month old as well as changed his formula to the 6 - 12 month formula. since doing this he wakes up every hour at night, seems to be in pain, passes a lot more stool and is in general unhappy. is this normal?

Not particularly: Any change in diet can introduce an agent to which the kid is intolerant/reacts poorly. Doing several things at once makes it hard to identify the troublemaker. A return to pre-change diet for a week can settle his system if this is the case. Gradual ( 1 thing every 3 d) can help find the problem agent. He may also just have some gut virus that is incidental to the process.