Why won't my mom let me spend time with my girlfriend?

We have been datin for a week and she has came over once and my mom liked her and said all tht great "she so polite stuff". Now when i ask if she can come over or if i can do sumdin wit her my mom flips n goes off on me wit tht "im gettin tired of u" type of ****. I want to make this relationship work but my moms kinda stoppin it ya feel me. so i need help. . .all answers will b great help =]