As well as fit, is it possible that you have incorrect filters fitted?
Particulate / dust & mist filters are often sold bundled with masks as they are cheaper than organic vapor / gas filters - if you're looking for protection when using Mr Color paint, you will need organic vapor / gas filters.
The cheaper particulate / dust filters are adequate for most water based acrylics, but Organic vapor / gas are good for everything that you're likely to encounter, including adhesives, fillers, primers, lacquers, enamels & acrylics (that aren't water based).