Have your master or secondary checked. Most likely nandun ang problem.
I also experienced the same problem before... I checked the clutch fluid level, ok naman. It means ok yung primary. The problem was the secondary(which i believe is the same case as yours). Dati nagpalit ako ng primary master, pero di ko pinalitan ang secondary... So I suggest that you replace both at wag pa-isa-isa lang kasi sabay mag wear out yan, pero in most cases mas madalas masira yung primary.I would suggest na sabay mo replace ung master and secondary, para isang gawaan na lang, madali lang naman palitan yung secondary,mga 5 minutes lang.