It can be a symptom of hypomania, but shopping alone doesn't mean that someone is hypomanic, especially if they have dominant features of depression. It can also be caused by a form of OCD. I'm not familiar with it being a symptom of depression, but bipolar disorder is very complicated, so I'm sure it's possible. I'm glad that you are going to talk to your pdoc about it because it's an ongoing problem for you and causes you a lot of worries.

Personally, I think buying the coffee was okay, but I hope you can reign in your shopping in general soon