Possibly some anti-emetic drugs or supplements might be worth looking into. An antiemetic helps prevent nausea or vomiting.
On the supplement side, ginger root is the classic antiemetic. Ginger blocks the 5-HT3 receptor, and any 5-HT3 blockers act as antiemetics.
Lemon essential oil (Citrus limonum) is a potent 5-HT3 blocker, and I suspect 5 to 10 drops of lemon essential oil taken internally (dissolved in a tablespoon of cooking oil or similar before swallowing) may have stronger effects in preventing nausea and vomiting than ginger, but both might be worth a try. You can by 10 ml bottles of essential oils for just a few dollars.
There are also 5-HT3 blocker drugs
like ondansetron sold as antiemetics.
At one point, 5-HT3 blockers like ondansetron were investigated as an ME/CFS treatment, to reduce fatigue, but unfortunately the results of clinical trials indicated that they did not reduce fatigue much.
Might be worth mentioning this nausea and vomiting symptom to your doctor, in case it is a sign of something else.