Did you "stipulate" (agree) that this commissioner could hear your case, by signing the court form before the hearing? That form is a "one-way door" once you've signed it, you can't undo it.
If you have information which you need the commissioner to look at before the next hearing, then you need to organize it, make several copies, serve a copy of it on your ex, file the documents with the court AND file a "proof of service" showing that you served it on your ex BEFORE the hearing, making sure that you get a "conformed copy" of the proof of service, so that if the clerk can't find it, you can show that you filed it..
You should NOT expect that court personnel will put together parts of documents for you, make copies of documents for you if you don't have enough copies, or organize the information you want the commissioner to look at. You should NOT expect that if you walk in with documents on the day of the hearing, there will be enough time for the commissioner to review those documents.
A stipulation is an agreement. I think your asking to have your issues heard in front of a judge. Once you have allowed a commissioner, or judge to hear a specific motion, a motion to reconsider has to be heard by the person who considered it. You are not likely to have him removed, perhaps you may want to find an attorney in your area who knows this commissioner, and can present your case in a way that the commissioner will understand. This may include filing objections to the court reviewing the letter by your ex. Find out why the court denied the medical reimbursements. There are specific steps to be taken before filing a motion for reimbursement of medical expenses.
Sorry, but I agree with other counsel.
My name is Stephen R. Cohen and have practiced since 1974. I practice in Los Angeles and Orange County, CA. These answers do not create an attorney client relationship. My answers may offend I believe in telling the truth, I use common sense as well as the law. Other state's laws may differ.. There are a lot of really good attorneys on this site, I will do limited appearances which are preparation of court documents it is , less expensive. However generally I believe an attorney is better than none.