If you haven't talked with your doctor about this, I urge you to do so. There could be a medical cause for your lack of appetite. Asking about appetite and weight gain or loss is always one of the questions they ask when doing a physical exam. Your hormones could be off. My first thought is that your thyroid may be producing too much of something. You could also have postpartum depression. Loss of appetite and weight loss can be symptoms of both of those conditions.
Also remember that you body shape has changed with the pregnancy and delivery. I envy your weight loss but also wonder why you want to be at 150-155. I'm 5-6 and at one time in my life weight 120-125 and am still told that is a good weight. For a few months I lost weight and went down to 115 and was told that was still acceptable. I liked being 115 but it didn't last. I'm up to 160 and feel fat. I'm also 67 and find that it is now difficult to lose weight unlike when I was in my 30-40's.
After many tests, I was told that there didn't seem to be a medical issue that caused my weight loss. I was anxious and lost much of my appetite. At that time, when I was anxious, I unconsciously decreased the amount that I ate and without realizing it, increased my activity, trying to get rid of my anxiety.
Could you be anxious? You're certainly busier than usual with a new baby. When I'm faced with something new I usually focus on the new stuff and forget to eat. Even now I can lose 5 lbs. before I realize that I have only been eating once/day.
Back when I wanted to gain weight, I ate all the good stuff that I thought I should avoid. Food like all sorts of ice cream in all forms. Dessert every day. Cake, cookies, pie. Unfortunately I got in the habit and put on 20 lbs. that I didn't want. I can "trick" myself into eating a healthy meal first by telling myself that I will eat healthy before I eat that ice cream.
If this were me, I'd rule out any medical or emotional cause for the weight loss and then buy some new clothes. lol Sorry, if this is what you didn't want to hear. I agree that if you want to be 150 then you should find a way to gain weight.