White spot on gum after tooth extraction. Extraction three days ago. Doesn't hurt. Looks a little like an ulcer. Is it an infection?

Probably not. After an extraction, especially this early into initial healing, the socket may have many different appearances. The tissue may appear white & sometimes food debris in the socket may also give this appearance. Unfortunately though we can't diagnose or tell you for sure whether or not you have an infection or other issue. Please see your dentist for follow up evaluation-part of Dr. responsibility.
Post extraction. Signs that f an infection would be pain, swelling, and bad taste. Healing tissue can look whitish. Continue to follow the post op instructions. Call the extracting dentist if you have concerns.
See below. If you feel this is a problematic area, contact the dentist that performed the extraction for a clinical evaluation. More important, have a treatment plan to replace the tooth ASAP.
Healing scab. Tooth extraction leaves a hole between the gums...it gets filled with repair material provided by the body. That is what you are looking at. it will slowly get absorbed and flattened and turn pink in 7-410 days. If it is infected(unlikely) it will cause increasing amount of pain. Lack of pain means it is healing normally!
Most likely not. probably a reaction to the manipulation of the tissues. If its not gone by the first follow up visit to the dentist then point it out to them at that visit. It should ot be growing three days post-op.
Early healing. Probably just normal healing, wouldn't worry about it. Follow the directions of the dentist that removed your tooth. Call him if you have a question.
Probably not. Whitish appearance of tissues may be normal healing. Signs of infection may include pain, swelling, fever, bad taste, bad breath, fatigue, etc. To be sure see the Dentist or specialist Oral Surgeon who removed the tooth for reevaluation. Also talk to your Dentist about plans to replace the missing tooth to prevent other teeth from shifting.