The best advice any of us can give you is to see your dentist. Only he/she will be able to determine what is going on with your tongue, and they may even need to refer you to an oral surgeon, but let's not get ahead of ourselves here!
I don't know how your breathing could be affected by the spots on your tongue unless it was swollen quite badly, but you said nothing about that.
You mentioned an allergy to sea foods and that you are normally very careful. Is it possible you ate some in a salad or other dish that you weren't aware of? Are the spots and itchiness a normal reaction if you eat sea food?
Please don't spend any more time worrying about this and see your dentist.
Peace
Greenlydia