Lothander only gave me one regular antidote and a large sheild. I killed the other guy at the Blushing mermaid and drank his special antidote. There is no message in the dialoge box or in the journal that says I have done it right?????

After engaging in dialogue with Marek (Lothander's friend-in-conspiracy), you should get something like 'poison removed' in the dialogue box. You don't actually have to drink the potion on his body.

Anyway you havent to complete this quest (though you should due to Eagle Bow). If you dont complete you WONT die, be sure.