Still not rolling?

October Mamas! When did your babies first roll over? My baby girl is just over 5 months and is STILL not rolling over. She rolls on to her side but doesn't seem to want to do any more than that and eventually rolls back on to her back. We have to hold her hand and help roll her over on to her tummy, but she hasn't done it on her own. She is pretty content once she's on her tummy, but needs us to flip her back on to her back when she is over it.  Anyone else's LOs still not rolling? We are trying everything but she doesn't seem interested. I have heard some babies can just skip this milestone altogether...