I have a shopping addiction.
Oh no!  The phrase shopping additiction usually has more of a psycho social perspective to it. 
I cannot go into a store without buying so much.
Oh I'm so sorry!  It's placed among other drug-free addictions like gambling, internet or video games.  What do you consider buying so much?
I go to the mall to find one cheap tank top and I leave with hundreds of dollars of clothes that I cannot afford, so I spend the next couple days stressing out trying to get money in my account to cover it before it cones through.
Sometimes that could be a Behavioral Addiction which is like a compulsion for a rewarding, non drug behavior - like a natural reward.  I'd say stay away from the mall!
Yes that is the best thing for me and online stores too!
Behavioral addiction
Behavioral addiction is a form of addiction that involves a compulsion to engage in a rewarding non-substance-related behavior – sometimes called a natural reward – despite any negative consequences to the person's physical, mental, social or financial well-being. A gene transcription factor known as ΔFosB has been identified as a necessary common factor involved in both behavioral and drug addictions, which are associated with the same set of neural adaptations in the reward system.
Psychiatric and medical classifications.
Diagnostic models do not
Shopping addiction
Shopping addiction is defined as the deficiency of impulse control which appears as the eagerness for constantly making new purchases of unnecessary or superfluous things. It is a concept similar to "compulsive buying disorder" and "oniomania", although these terms usually have a more clinical approach, related to a psychological individual disorder of impulse control. The phrase “shopping addiction” usually has a more psychosocial perspective . or it is placed among drug-free addictions like the addiction to gambling, Internet, or video-games.