I've recently experienced similar problems on three separate uses of crystal, where sometime after the drug has come up I'll randomly feel very queasy/nauseous and uncomfortable to the point I have to distract myself from it. I will inevitably throw up the contents of my stomach and anything else I eat that day; I even have trouble keeping water down. It's very uncomfortable, and unfortunately usually lasts the next day after using, although much less severe...if it's just nausea
then I'd recommend OTC anti-emetics, I take gravol and meclizine
hcl which provides some relief. It's not serious, many, many crystal users experience it, and most likely it has more to do with a lack of tolerance/experience of meths effects. Hope you can kill the nausea!