Probabtion

I am with current employer just over 4 years and have been permanent for 4 years. Last November I was given a new job at the same level. I didn't get any more money etc, it was a sideways step. However, as it was a new position for me I had to sign a new contract. This contract had a probabtion period of 6 months which basically says my performance will be reviewed after this time

Things haven't been going too well for me in this role and I am finding it hard to get used of the role. My boss has had one or two chats with me about this. there never have been issues with my performance before.

My question is what usually happens with probabtion period for something like this. If it is decided I am not up to the job what rights do I have - I understand that i can be fired but I'm guessing the four years service count and not just service since i started new position in November?