The most probable cause is the hormonal change that the body undergoes after conception. Other contributing factors are mineral and vitamin deficiencies in the body.
You can prepare tea out of red raspberry leaves and drink it first thing in the morning to lower your vomiting tendencies.
Whenever you feel like throwing up, just press it close to your nose, and watch and feel the difference. You may also try out drinking some lemon juice.
You must keep a small container with fennel seeds nearby and chew on a few of them whenever you feel nauseated or dizzy.