What should i do for painful aphthous ulcers?

Prevent trigger: See prior answers relating to these for much more discussion. Each person usually finds that certain things trigger them, e.g. Citrus fruits, lack of sleep, weight loss, iron, vitamin B12 or Folic Acid deficiency, trauma, braces. There are some systemic diseases associated with these: crohn's, behcets, celiac disease. Also think of hot drinks. Oragel topically or antiviral rx early on may help.

A miserable issue: For sure. Discontinue toothpaste that has sodium lauryl sulfate, limit acidic foods and try to avoid trauma of oral tissues w toothbrush/utensils. Look for zilactin products in pharmacy to apply. Best medicine is rx steroid in an oral bandage delivery called "orabase". Lasers can help if your dentist has one.