Life long usually. Most shellfish allergy is life long. Repeat testing and possible oral challenge may help determine if the allergy has resolved.
Long time. Peanut, tree nut and shellfish allergies tend be very long lived allergies.
Yes. Lobster is related to shrimp and crab. Each of these is a common cause of life threatening allergy. If you are having symptoms after eating any of these you should be evaluated by a board certified allergist. Do no eat any shellfish until you have been cleared.
Seafood Allergy. Allergy to any food, in this case lobster will cause symptoms of oral itching, lip or tongue swelling, hives, breathing difficulty and/or throat closure etc. Food allergy is diagnosed with clinical history followed by skin or blood test and that information helps establish the diagnosis and severity of the allergy.