Does anyone have this problem?

My four month old used to take three naps during the day. She took a small cat nap in the morning, then a lunchtime nap and then another short nap in the late afternoon. Now she refuses to go down for the two catnaps. I can tell she is tired, but no matter what I try to do she will cry and cry and cry until I pick her up. Has anyone else ever had this problem? What can I do?