Why can't I do any tricks on my skateboard?

I've been skating for like 2 years I still cant get any tricks down except for ollies. i practice alot...but i still cant do anything for some reason. i cant even ollie a 2 stair. (cant even ollie while moving). when i do kickflips i only land them with my front foot..i cant do any other tricks. please tell me what i should do. thanks