Your toothbrush can harbor lots of bacteria and germs. Regular replacement of your toothbrush is important and should be done every few months. In between regular replacement if you get sick this may be a good time to change out for a new toothbrush. There are ways to clean and disinfect your toothbrush as an alternative.
You can rinse your toothbrush in a mouthwash is not very effective at killing the germs. You can soak your toothbrush in rubbing alcohol and then rinse thoroughly before using. Hydrogen peroxide is only effective against some of the germs, and can be irritating to your gum tissue so is not a great alternative.
I have had patients who put their toothbrush in boiling water or the microwave, but the risk is burning yourself, melting the toothbrush and making a big mess in a pot or the microwave. In truth replacing the toothbrush may be the simplest solution. If you have a professional toothbrush like a Sonicare or Oral B you can simply replace the head of the brush, or use the special cleaning device that is part of the charging base to disinfect the brush head.