Have you attended local meeting of La Leche League? Their Leaders are accredited as breastfeeding peer counselors, and while they are strictly volunteers, they really know their stuff. Many LCs get their start working with mothers and babies through LLL. It usually takes several months to a year to become a LLL Leader, but you can work at your own pace. Lots of the required reading would likely be of interest to you. You can find your local LLL group at www.llli.org, if you're not already involved.
The highest level of certification for an LC is IBCLC. The IBCLC exam is given once a year, in June, it costs about $400, and there are several things you'd have to do to qualify to take the exam. If you look at the Web site for the exam (I think it's ilca.com, but if you Google it you'll find it for sure) it will give you the nitty-gritty. There are three or four "paths" to qualify you to register for the exam, and they are either taking several lactation-specific courses or having lots of in-person experience helping breastfeeding mothers. Many LLL Leaders qualify via this "helping" path, since just two or three years of accredited, active Leadership with La Leche League can qualify someone to register for the exam.
But the IBCLC exam is like the bar or the CPA--just knowing some basic info won't be enough to pass, because a lot of the test covers special situations (prematurity, medications, special needs, etc., etc.) so you'd have to plan to do some kind of test-specific study course or study prep beyond whatever classes or experience path qualified you for the exam to be ready for it.
Often IBCLCs are RNs first, but they don't need to be. Often, IBCLCs work in hospital settings and hospitals like to hire people who are also RNs, but again, it's not technically necessary. WIC also hires IBCLCs for their breastfeeding counseling programs, and really pregressive pediatricians have an IBCLC-certified LC on staff, but that is a rare gem.
There are less-intensive ways to become qualified to help breastfeeding mothers. There are many courses available online and as electives in university medical programs to become a "breastfeeding counselor" or even a "lactation consultant" who is not IBCLC-certified. But the International Bureau of Certified Lactation Consultants is considered by most lactation professionals to be the most influential certifying credential, and the one most sought-after among medical professionals.
I really recommend you get in touch with LLL! They are strictly non-profit but are considered by many to be the foremost breastfeeding organization in the world. It could be a more engaging path to the IBCLE than a breastfeeding theory class.
Best wishes!