Tiny poops occur when the guts slow. As RavenousDragon said, this can come from several different causes (stress, pain, teeth problems...). This is not an illness in itself, it's a side effect caused by another problem. There may be no need to treat the guts in themselves as long as they don't stop (that your rabbit is still pooping) and that your rabbit is eating a healthy amount (his own body) in hay. BUT you need a vet to understand what's the underlaying problem and to treat it as well as the pain your rabbit is probably feeling.
I also don't really like the brown liquid you mention. Small poops can indicate quite a lot of things, not necessary life threatening, but a discharge to go with it could indicate an infection. In any case, I wouldn't wait before going to a rabbit savvy vet. Sick rabbits can often be saved if they are treated fast but their condition tend to worsen pretty quickly.