The easy answer is to not allow yourself to buy things the first time you get an impulse. Write down what the thing is & what store you found it in, on a piece of paper you carry with you.
If when you look at the list the next day, it still feels important, then you probably do really want or need it. I have found, in using this method myself, that I rarely actually go back and buy the things that seemed so important the day before.
Now here's the hard answer. From our previous correspondence, I know that you are trying everything you know to get your husband's attention, which may be part of the reason you are buying things to make yourself feel like you look more attractive. But since you already know that you don't really need these things, and you also know that spending this money will get his attention, you may unconsciously be continuing to spend money to get him upset---because then he certainly pays attention and focuses on you. Sometimes negative attention feels better than no attention at all. But these fights will only drive him further and further from you.
Please remember to get and read the book I recommended last time.
It seems like your issues are building up, and affecting different areas of your life.
If you have health insurance, I would recommend that you find a local therapist to work on your self-esteem issues, and to help you take active, positive steps to improve your marriage. Here's a link to help you find a therapist: http://therapists.psychologytoday.com/rms/
It sounds like you are pretty isolated at home with the baby...it would be wonderful for you to have someone to talk to in person to give you that ongoing support. I am happy to continue our correspondence, but I think you need in-person support as well...it can be so lonely being a new mom.