I clench my jaw a lot at night. do you recommend a more expensive, professionally fitted mouthguard or can i save money and use a self-fitted one?

Try it.: It is best to get into see the dentist, but n the meantime, you can try a self-fitted mouth piece. Make sure you stay away from chewy foods and give your jaw a rest.

Can't hurt to: Try the cheaper option of a self fitted night guard first. It's important, if your are a bruxer(clencher), that you be able to wear the guard consistently. So, if the home version is tolerable comfort wise, you'll likely be fine. If it's just not comfortable and you're not able to consistently wear it or your symptoms are worse, consider going the route of the more expensive professional fit.

Time will tell: Without an actual examination, I cannot give specific medical advice on your particular health, like if you have TMJ, a deformed mouth/jaw. You will want to have regular dental check ups. GOing with the cheap one (martial arts stores carry them) may work or there may be discomfort or the teeth may continue to show wear.