I have a small blister in my mouth that is lightly bleeding right now (I can taste the blood). Should I check with my doctor or dentist? I'm so worry

See your dentist. Most minor ulcers/blisters/traumatic injuries in the mouth heal on their own within 7-14 days. Keep the area clean with warm salt water rinses and avoid spicy, irritating foods. If you feel overly concerned or the condition worsens than have an evaluation by your dentist.
Harmless mucocele. Usually they're not a problem and will go away on their own. If concerned see your dentist for evaluation and surgical removal.