Nausea is a fairly common side effect for most opioids. It tends to happen less frequently and less intensely after you develop tolerance but will likely return anytime you take too much. Some people are just naturally more prone to experience nausea unfortunately.
Some options:
1) you can try using less heroin, you might be taking too much for your tolerance level
2) some people find using cannabis helps (I don't, I hate the way it makes me feel so I find it ruins the opioid experience)
3) you can try the usual home remedies for nausea like ginger, peppermint, etc
4) take some Dimenhydrinate or other similar OTC antihistamines that are reported to help with nausea / motion sickness
5) prescription drug ondansetron (zofran) is suppose to be good at preventing nausea