Tonnerrebird thanks for the ton of info, that was a great help. I thought I would sound out the PT forum just for some advice. I have booked an appointment for Jack for Wednesday to see the vet, and will post what happens here for general info purposes.
I thought of worming him first before going to the vets as he finds it very stressful riding in the car in the carrier and usually has a panic attack. I hate putting him through it so wanted to avoid going, but I am concerned about him too much and have to take him, I am going with my fiance this time instead of my mother so I can sit with him in the back of the car and my fiance can drive. I think he may be a bit calmer if I'm with him and he can see me.
He has continually lost weight over the last two months, and usually vomits saliva a few times a week. He's eating normally, his toileting is normal though very smelly, and he's fine in himself. But his coat is getting quite bad and he's becoming very thin. His stomach gurgles a lot I've noticed, like has wind (gas) or indegestion.
Before we adopted him, he was left to starve, and was very malnourished, so I think it may be a intestinal problem with him.

I'll let you know how he got on on Wednesday.

Thanks again
Kate