Hi, Stop using birth control pills and call your doctor at once if you have a serious side effect such as: sudden numbness or weakness, especially on one side of the body; sudden and severe headache, confusion, problems with vision, speech, or balance; chest pain or heavy feeling, pain spreading to the arm or shoulder, nausea, sweating, general ill feeling; sudden cough, wheezing, rapid breathing, coughing up blood; pain, swelling, warmth, or redness in one or both legs; a change in the pattern or severity of migraine headaches; nausea, upper stomach pain, itching, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); swelling in your hands, ankles, or feet; a breast lump; or symptoms of depression (sleep problems, weakness, tired feeling, mood change) And weight gain is again due to progesterone. Plan B has frequent use of emergency contraception can result in side-effects such as menstrual irregularities, although their repeated use poses no known health risks.