Hi Micky,
The yellow mustard poop is normal. I don't have personal experience with elimination diet but here are some things you may want to consider:
Diary can be found in many products, you will need to read labels very carefully. It is true that it happens very often to be the culrit for baby fussiness. It also is in a chocolate :cry:, except for dark bitter varieties. If you already cut out diary, the soy also may be the thing that causes discomfort. If you like soy milk, try instead rice dream.
There is a list of foods that are theoretically inducing gassiness in breastfed babies, first are beans, broccoli, cabbage, peppers, spicy hot foods, especially Indian, I think. The list goes on but the point is that you should eat a healthy and a balanced diet while nursing and you can't just eliminate everything. For us strawberries were a big offender. I really can't think of anything else at the moment.
The second thing, I agree with your doctor, his system is not mature yet and thus all this fussiness, albeit extreme, I admit. I agree that for you it is not easy to just watch your baby being uncomfortable, but it will probably pass soon. He is now 11 weeks, he should be getting better within short time.
As for accidental parenting, I think, when they are so young and uncomfortable, you should do what works at the moment, you need to survive :lol: . For us, first 3 months were the toughest, from then on, I got a hang of it and my dd was easier to handle, too.
There is another thing that crossed my mind. Even though, you say you are sure it is gas, what is your baby's personality? My dd was/is a spirited angel and spirited relates to sleep in our case. That means, she always has been fighting sleep, even as a newborn as if she thought she would be missing something if she went to sleep. Sadly, this still continues today. But, the thing is, when she was a newborn, and before I even read BW, I would nurse her, wait till she was motionless, quietly, without breathing, I would transfer her to crib and ... she would awake! She would then start flailing her arms, scratching her face and so on. That could continue for a long time each night. From today's perspective, I wish I swaddled her and knew more about babies :oops: .
Anyway, I hope your ds gets better. Keep us posted
.