I just drove across the state. There was minimal traffic so I drove in 5th for about 3 hours straight. After coming off the highway and merging off to a stop light, my car wouldn't go into 1st, second, or even third. I had to absolutely JAM the shifter to finally get it in. My first thought was clutch, although I am also considering low transmission fluid and lack of lubrication of the gears that weren't being driven. It is no longer doing this, but occasionally similar things happen where I can't seem to put the car into gear. Any thoughts? Anything helps

Sounds like a clutch problem to me. I've had them do similar things to me before.

Probably not due to anything inside the transmission.