Hey Niglet - welcome aboard.
I think the key to exercising successfully is to find something you love to do, or mix things up.
Do you walk with an mp3 player or anything like that? Can you find a training partner? Sometimes having someone to walk and talk to, and who is expecting you to actually BE there is quite helpful. Or would you prefer to play a team sport like netball? Or how about group exercise classes at your local gym?
Exercise doesn't have to be boring - you just have to find what you enjoy doing.
Can you fit more incidental exercise into you life? E.g. walk instead of drive to the station, walk to the supermarket etc.
I personally hate weight training. I know I should do some, but I find it sooo boring that I just avoid it. So instead I incorporate a bit of resistance training using my own body (push ups, tricep dips etc.). If I did weight as part of personal training I would enjoy it, but that's too expensive for me right now.
Be aware that the type of interval training you're doing is where people are most likely to get injured.
If you're interested in slowly building up your fitness, consider the Couch to 5km program
which mixes running and walking until you're eventually able to run 5km without stopping. Many people have had success on this program and some girls here on the forum are doing it. However, that might not be what you're after.
Just keep moving! And don't be lazy...
SW: 74.3kg - 1/1/09
CW: 71.1kg - 3/5/09