Hi, to what extent you can be your own therapist depends on all sorts of things from what you're dealing with and what the causes are to how easily you can be self-honest. at the moment, i have no choice as ive found it hard to get a therapist, and have been getting somewhere, though sometimes it doesnt feel that way. for me because of what my issues are, speaking to a therapist about stuff is a whole hurdle in itself, but one i need to get over.
as for using your own understanding of stuff, of course you can try to understand things better, but applying knowledge to information is one thing - with doing self-therapy it involves applying what you know to emotion, and how you do has a lot more to do with how well you can access that emotion. having the support of a therapist isn't just about an outside perspective its also about support.
for free CBT, if you search "moodgym" on google there is a free online CBT programme there, its a study on using cbt to improve mood, but im guessing you can use it for all sorts of things other than mood, so it might be worth a look.
also, these forums are not a bad place to chat. there are some really great people here.

Edited to say good luck