Jonathan,
In the UK there's no real distinction between an amateur or professional photographer, except the latter decides to charge money and sets up in business. Over time the professional just gets more practice at it, learns a few tricks and techniques, and is probably more consistent, rather than "better".
Whenever an amateur starts taking his photography seriously ( as in your case), the results are usually frighteningly good. The photographs you have taken all have a creative eye, but you probably wouldn't be doing it if you hadn't got that.
If you want a goal, why not consider submitting to a picture library. This was once " strictly for professionals" but for many companies this is no longer the case. There are several on-line libraries who can deal exclusively through the internet - contracts, submissions, sales etc .
I've used this site but I'm sure there are others.
www.alamy.co.uk
It's really a numbers game. You need to submit tens of thousands of images to make "a living" ( even 1000 will only get you about 2500 Danish Kroner per year), but even for small numbers its a great kick to get paid for your images. Don't expect to get rich. The brilliant pictures aren't usually the best sellers.