Are you still getting your period? Gaining weight can make you more tired. It wont make your breast tender unless its alot of weight at once. Like 25 pounds or more in a few weeks. You do not get sick from gaining weight. You dont get swollen ankles from gaining weight, those come after gaining weight. Go to the doctor and take the pregnancy test there because its more accurate than the store one. If your not pregnant they can evaluate the weight gain. It could be something else like thyroid.