Definately, I have 2 boys with DS1 I had M/S for a couple of months but nothing too bad and with DS2 I wasn't sick at all.

As for the different father factor I'm not sure but have wondered that myself.
DS1and2 have the same father but I'm now repartnered and pg with #3 and I have only just recovered from the HORRENDOUS morning sickness, I was bedridden for 9 weeks with a bucket much sicker than I was with DS1, permanent headache and vision problems and low blood pressure.
I did wonder if the different hormones from having a different dad could influence it.

As for the sex of this one well I don't know and I'm not going to find out, I want the surprise so I'l have to let you know in about 4and a half months