Trouble Changing Gears

This problem started 3 days ago. All of a sudden its hard to put it into any gear and change gears while driving. The problem seems to get worse the longer i drive. For example.... When i first start driving you can tell their is a problem but its not to severe, then after about 20-30 minutes of driving i can barely get it to change gears. So what could be the problem? What things can i check? Thanks
 
Can you be more specific?...I was thinking three possibilities.

1. The synchos in the tranny are worn.

2. The TOB and/or clutch cable is worn causing the pedal to be very stiff.

3. The stop gates on the shifter need to be adjusted so the tranny can go into gear.
 
clutch cable is stretched out too much causing the clutch to partially disengage and thus hard to put into gear. possiblity?? do you have a adjustable clutch quadrant and if not it might be time to invest. just my opinion. hope it helps.