What triggers nausea while breastfeeding and also pregnant?

Is there anything I can do to avoid this? Pregnant with number three and still nursing number two who is almost 9 months. I am not going to give up nursing until she is at least a year maybe longer. Other then changing positions nursing can I do anything? Waves of nausea seem to come on very strong during and after feeding my baby. Its worst then I have ever experienced actually with my past two children.