Upfront disclosure....I have a B.A. in Accounting.
That being said, I think experience speaks volumes. At the same time it may be worth your time and money to take some basic acctg classes. Perhaps you have a junior college or technical school close by where the tuition would be cheaper. I know of many very successfull bookkeepers who DO NOT have 4 yr degrees, but opted for 2 year technical degrees. You have to be prepared to answer technical questions and your clients are relying on you for the answers. If you've learned plenty on the job then maybe you already feel comfortable with this.
Another thing is....if you start your own bookkeeping business be prepared to have people ask you about tax preparation.

ANYBODY, I repeat, ANYBODY can become a tax preparer. I worked one season for a nat'l tax prep co. and a lot of us were seasoned accountants but there were MANY that were clerks at a local convenience store or school teachers or laborers, etc.
Last, but not least, I personally would learn Quickbooks inside out and backwards!!! In fact, you can get certification in QB. That cert. is quite an investment (forgetting the exact cost) but it may payoff in the long haul depending on your area. Just look at QB's official website.
I put a lot of thought into building a homebased bookkeeping business a couple of years ago before I landed the perfect part-time job. Please feel free to ask more questions.