Hi A.,
I initially lost weight while BF, but I did develop hypothyroidism, so it quickly tapered off. Make sure your doctor measured thyroid antibodies (few do). If you have antibodies, you can be going towards hyper and still have normal tests. Pregnancy and childbirth can trigger this.
That all said, I'll a few comments on your diet - it does not seem nutrient dense overall and you don't seem to be eating too much protein, nor do I see healthy fats. Mother nature makes sure that the breastmilk gets all the nutrients the baby needs and will "steal" from the mother, so to speak, if the daily diet isn't providing everything.
I would ditch the chips - there's virtually no nutritional value to them. Also, the breakfast cereal is the same. I can't even remember what a nutty buddy is, but again, it doesn't sound like it provides too many nutrients that you or your baby need. I do recommend this mini-meal model, but you need protein with every meal - either healthy meats, eggs, nuts or bean/seeds. Also, having a smoothie everyday with protein powder (I like pea, rice or hempseed) and alot of fruit will give you some condensed nutrients. Also, add some healthy oils to your diet - olive oil, fish oil, and something like flax seed oil. And, if you can tolerate butter, it is very healthy. Folks are afraid of fat, but eating the healthy fats is a necessity - you just want to make sure to balance the fats in things like your chips (Omega 6s) with the other oils (Omega 3s and 9s). Your consumption of these is also very important for your baby's health - the 3s are very important for brain development and are not made by the human body. It's the transfats and the fats in commercial/non-grassfed meats that you want to avoid. The fats in grassfed and free range meats are different and far healthier. Eggs also are an excellent source of nutrition.
Also, what size are your water bottles? Even if they are 16 oz., that's really likely not enough to compensate for both your body's daily needs and that needed to provide the breastmilk. Your weightloss may be around 10 lbs of water in my experience - I was on an antihistamine for allergies and I lost 15 lbs in 3 months one time.