Why not wait to wean him until AFTER he turns 1? What are you trying to accomplish by starting early? You complain that your baby is fussy and irritable. That should be a big red flag to you. The AAP has a reason for their recommendation of waiting until babies turn 1 before starting cow's milk. It is because babies little systems can't digest the protein's in cows milk. The intestinal lining of a baby is slow to mature and lacks the necessary enzyms and bacteria to help break down the proteins in cows milk. If you give your child milk too early, many babies will develop diarrhea, bloating, and abdominal pain, because of their inability to digest the proteins in milk. Diarrhea, bloating and abdominal pain = fussy baby! And guess what happens when you have diarrhea? All the good enzymes you had in your intestinal lining get flushed out and your body has to build them back up slowly over time. When you don't have all those good enzymes, you just keep having stomach issues. It's a vicious cycle. By giving your baby cows milk too early, you are perpetuating the problem.
The process of making cheese, yogurt, etc. is different than milk. In the process of making those products, many of the hard-to-digest proteins are broken down which is why many babies can eat cheese or yogurt, but not milk.
If you haven't already done so, I would highly recommend checking with your pediatrician before starting this too early. If your baby has had a history of stomach problems, I cannot imagine why you are doing this before your baby's little body is ready.