Is there a way to keep hair dye from fading?

Every time I dye my hair, it seems to fade after just a week or two. I'm a natural reddish brown and I dye it a darker version of the natural because my hair tends to look dull and almost grayish sometimes. I take a shower and do the dye about 1 1/2 days after when my hair becomes dirty. I leave in the dye for the time the instructions say, sometimes even 5 or so minutes longer. When I rinse, I get my hair a little wet to lather and rub in the dye more, as the instructions say as well. I use the special conditioner given and even by the colored hair shampoo and conditioner (although I'm not so sure I believe those special titled shampoos really do what they say). After a few weeks it either looks light brown or red, or even back to the way it was before dying. My mom bought a package of red and blonde to do her hair, but she has recently decided to finally let her grey go. I am thinking about using the dye she has bought for a different look. I am getting sick of wasting my time and money and frying my scalp and hair for just a few weeks of color. Is there anything I can do to keep the color in? Thank you!