I am assuming that you are using affirmations in order to change a belief, a feeling or whatever else inside of you that you do not like.
For affirmations to be effective you will have to firstly remove the block or the root of the problem that is causing this discomfort. Because if you do not really believe the truth of that affirmation and feel it completely inside of you, you are then resisting it. You can cheat yourself of how you are feeling. You can NOT use logic to solve psychological (feelings) problems. They are two different things that have to be developed in parallel because if somebody develops the logical part much more than the psychological then this person becomes what we call "eccentric"
A quick way to remove any discomfort, is to welcome the "feeling" (the same way you welcome your kids) you are experiencing on your body and just let it go the same way air bubbles rise up from the water. Just repeat the same procedure 3 to 4 times and then check how you are feeling. You have nothing to lose
Good Luck