2001 Ford Ranger Clutch won't engage into gear

It has been happening on and off for the past 6 months. My clutch would not allow me to engage into gear, especially when is cold outside. Usually I just pump the clutch and that fixes it. This morning, although it wasn't as cold as it has been, the clutch started going well, from first to second and then when i tried to go into third it did it again. It felt like it had a little backlash and it stopped allowing me to engage into gear. I waited for a minute and even added some DOT-3 fluid, but did not work.