Pen pressure not working

I have a Wacom tablet and I use the download version of FlockMOD, so whenever I use the pen tools or others , the Pen Pressure gives me like a really ugly line (?) Like it doesnt go smoothly from small to big, Instead it does it like small to suddenly big. aka being the lines and not sharp but they are VERY chunky. I have reinstall my tablet but that doesnt seem to be the problem. So what can I do? Please help!