I had HG with my first 2 pregnancies. I've actually been pregnant 5 times & had HG 3 of those times. With my girls I was severely sick for about 5 months then it started to ease.
With DS I was just sick like normal ms. It was so much easier!! No hospital stays, vomitting 20 or so times a day down to maybe 2!
With me I'm pretty sure it is the sex of my babies that has the effect. Girls give me HG, boys don't!