Crown on my tooth 4 days ago: Now I have blisters on my tongue and inside my gum.

These blisters you are describing may be apthous upcers (Canker Sores) which are painful open sores in the mouth (usually less that 1cm) that look like white areas surrounded by a bright red halo. They can manifest as a single bump or a group of bumps. These sores usually appear on the surface of the gums, roof of the mouth, cheeks, lips and tongue. These sores are completely benign. Symptoms start with a tingling or burning sensation, and progresses to a more painful bump or red spot. often times they are brought about by emotional stress, hormonal changes, menstrual periods, food allergies, spicy foods, and dietary deficiencies of iron, B-12 (cobalamin) and Folic Acid. Though, as in your case, these sores may occur after an aggressive tooth procedure or dental work, or by biting one’s tongue when numb.To be safe if the blisters do not resolve on their own within two weeks they should be evaluated by your dentist.

Sounds like you may have apthous ulcers which can be caused by stress or even dental work . They are completely benign buy can be painful.  They should resolve in 3-5 days.  I would avoid any spicy foods, citric acid, etc.