Need help with uneven tyre wear

Hello, I have had my car for 5 years now. its a Ford Fiesta 1.4i Ghia (EFI) 1994-1995.
The problem i face is uneven tyre wear, its on the inside of the tyre.(Front Tyres both sides) and it keeps happening to me. this is my 4th set of tyres in 5 years. the lower arms have gone and been replaced 4 times too. the last time i got new tyres was in march 2010. 6months ago. at that time i also had to replace the lower arms. then i got it all tracked and set. (again). today after i checked my tyres conditon noticed the inside has started to wear. and by standing infront of car i can see that the wheels are facing out slightly.
i cant understand why it keeps happening. im not a fast driver, i take it very easy and layed back. i look after my car very well.
i would greatly appreicate any help and advise. if you need anymore details pls ask.

thankyou

We need more information. How much air pressure are you carrying? Is it the top of the tyre that is facing out or is it the front of the tyre? You shouldn't have had to have the lower arms replaced 4 times in 5 years. How many miles/kilometers do you drive in a year? Why are the lower arms replaced so often? This is unusual unless the roads you drive on are extremely rough. I think you should take it somewhere else to get it tracked. I don't think that whoever has been doing it knows what they are doing. I do work on front ends and you should only need it tracked about once every 5 years with normal driving. Also, control arms should last at least 10 years.