Are you seeing a medical professional about the hives? Hives can be caused by so many things, and a lot of times you have to invest a lot of time (yours and your doctors) in narrowing down the cause. Sometimes it's stress, sometimes you have to work with an elimination diet, or logging everything your are doing and come into contact with- in order to figure it out. If you aren't seeing a doctor about them currently (even if you have in the past)- get to one and keep pushing until you get some answers.
As far as what helps them- that also seems to vary. What types of treatments have you tried?