Many people have reported that bettafix destroys the organ they use to breath with yet most petshops will recommend it for bettas. I would stop the bettafix treatment.
Most bettas won't even look at a pea - its more for goldfish. I think.
Go with epsom salt at 1 teaspoon per gallon.
However, most fish I have had with SBD act normal - minus swimming issues. SInce you said he has not eatten for 2 weeks - that leads me to think maybe it's not swim bladder disease but something else like an internal infection or parasites maybe.
do you have a picture?