95 GA Trans Trouble

alright sorry if this has been asked before, but here we go.

Today when i was on my way to school my car started acting funny. When i accelerated, the engine would rev as if it was in neutral. I kept accelerating and nothing changed. Then i shifted it down to 2 and 3 and it ran somewhat descent. I asked a few of my buds what they think it is and several people said it was the transmission sticking. I thought it was due to low fluid. So when i came home i added the proper fluid and now the engine is making a loud knocking sound and the engine suddenly became loud as hell but the gears shift fine.

any ideas?

thanks for the help.