If your flaxseed oil tastes bad, take it back for a refund. Most flaxseed oil is now sealed with nitrogen over the top of it to keep it fresh longer on the shelf, but as soon as you open the bottle the nitrogen escapes and the oxygen from the air will start to turn it rancid. Storing your oil in the freezer will slow this process down tremendously. Unless you can get through a bottle of the stuff in 2-3 weeks I suggest you store it in smaller airtight containers in the freezer.
And definitely shake the stuff....