Need some advice,

I have a three year old who has been crying constantly. She has been doing this for the last two weeks on and off. I've had her since she was a baby and she's always been very needy. She is very manipulative and if things don't go her way she cries. She went on a vacation just her and her parents for a week, so had all the attention in the world. Since she has been back, she has been crying. I've done the rewards sheet and it doesn't help. She cries out of the blue, so it's not that we are doing an activity she doesn't like and starts to cry. There is no rhyme or reason. ( Mom is at home with baby sister, so she wants to stay at home too) She wants the attention. I've tried ignoring the behaviour, but it doesn't change. If I tell her to go to bed and get up once she is in a better mood. She will stay in bed all day. She doesn't want to participate in activities. Any ideas?