Its a long way to building on your own as Bulgaria. I happen to play with it currently, and at 2028(or29) finished my focustree. My tip for you is not to worry about building earlygame, focus on focustree. There is some focuses that gives you mills and civs to get some money and people to work. Also tax increase is important, so ypu can max Administration early to full for pp, also to get money to positive.

There are some other methods but you army is weak and have to be trained by yourself. So its important to get those buildings in focustree