Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Try 24mm for awhile before buying these!

I bought the Medela pump and on the first day of use felt pain and discomfort while pumping. I thought I am using the wrong size breastshield and I ordered these the same day. It took almost one week for the product to arrive and by then I kept feeling better everyday with the 24 mm shields. I didnt notice an increase in supply or improved comfort with these 21 mm shields. I just needed to get used to the pump. Do wait for atleast a week to see if the shield size is the problem.