What the heck happened to my little girl?????

OK....my daughter, who will be 4 months on the 15th has just about got me over the edge. She started sleeping through the night at about 2 months old..give or take a week. She has never really slept during the day..maybe an hour here or an hour there. Sometimes(maybe once a week) she will take a 3 hour nap. For the last week and a half....I am lucky if she sleeps more than 20 minutes 3 times a day!!!!! Also, she started waking up at 4 in the morning...just screaming...I mean SCREAMING!!!!!! If I give the pacifier to her, she will settle down for maybe 45 minutes. Well, actually she always wakes up screaming now....no matter when it is. This is a baby that usually goes to be between 8:30 and 9:00 and sleeps until 6:30 or 7:00 the next morning., and wakes up fussy. She is definately eating well. She isn't sick, as far as I can tell....so what could this be...any ideas or suggestions at all would be wonderful!!! Thanks in advance.