Hello Tom. Five things:
1. Your new blog theme looks good.
2. You've tried this so many times before and I want to congratulate you on persevering.
3. There is no longer any 'off topic' or 'showcase' forum here and these forums are now for technical questions.
4. The fact that you never keep going is probably more to do with you than with blogging, and only you have the answers to your own self. Only you can find out how you can get into a habit of anything. But here's a tip: have a think about the things that you do and which you don't keep doing, and then have a think about the things that you keep doing - and try to work out if there is a pattern to the ones you keep on with. Then try to apply that to your blogging.
5. You need, with blogging, to do more than just write in your own blog. You need to connect with other bloggers. You're nearly 17 - so why not look for other teenage bloggers, comment in their blogs and then in time they'll come and comment in yours. That way, you'll get feedback and support from your peers and you'll be much more likely to keep going.
Good luck. :)