My DD started crying like that when she was about 4 months. It got to the stage where she would start crying as soon as we walked into her bedroom. One of the things that helped was that we stopped wrapping her, and put her in a grow bag.

We also introduced a settling time in her room out of the bed. We made sure she was changed etc, put her in her sleeping bag, then we sat in a chair and read her a book, before putting her into bed. For the first couple of months we only read the exact same book, everytime, before every sleep. It was amazing and still is working now 5 months on, except that we now read different books.

Maybe something like this could help.