Can you be charged with an assault for pushing someone.

Yes, you can be charged with assault due to such contact w/ others. The govt has the burden to establish non-consensual contact and other elements of the assault charge(s) beyond a reasonable doubt. You claim that self-defense may be an option in these proceedings. Better get a lawyer to assert this defense on your behalf. Many assault cases feature evidence that consists of nothing more than the accused's word vs the alleged victim's word. Therefore, prosecutors are exposed to acquittals unless their evidence is solid, in which case a plea arrangement is in order.

First, you must realize that you should never post such incriminating details online. This or any internet site is not private. You have a Fifth Amendment right against self incrimination. Use it.