For vomiting i would recommend trying a OTC anti-nausea drug first such as dimenhydrinate or meclizine. If those don't work go see a doctor. I would recommend trying the following drugs for nausea and vomiting related to opiate withdrawal:
1. Promethazine which is OTC in some countries and is a anti-histamine that is supposed to work rather good for nausea
2. Metoclopramide which is a strong D2 antagonist that also empties out your stomach contents quicker. Only take it for as long as you absolutely need to though because it can cause tardive dyskinesia if taken for a long time.
3. Prochlorperazine (trade names Stematil, Stemazine, Compazine, etc) is a old typical anti-psychotic now almost only used for nausea and vomiting.
4. Chlorpromazine (trade names Largactil and good old Thorazine

) was the first anti-psychotic on the market and is a phenothiazine like promethazine and prochlorperazine but half as potent in it's anti-psychotic action as prochlorperazine. I have found it to work fantastic for nausea and vomiting caused by anything including opiate withdrawals. It has stopped my nausea when nothing else has. Doctors often use it in ER settings along with morphine or some other opiate to stop the nausea from things like migraines and to increase the effects of the opiate. It's also rather sedating so it will help you sleep.
5. Methotrimeprazine aka Levomepromazine (trade name nozinan) is a weak typical anti-psychotic that is about half as potent as Thorazine in it's anti-psychotic action. It is mostly used these days to treat severe insomnia and nausea and vomiting. It works very well for me but it is hands down the most sedating drug i have ever had. It makes seroquel look like dextroamphetamine by comparison

. 15mg's which is not even close to the dose used as a anti-psychotic will knock me out for about 12 hours.
6. Scopolamine a drug that is a very strong anti-cholinergic that is derived from the Belladonna and Datura plant. It is available in Canada anyway OTC in a transdermal patch called Transderm-V. The patch lasts for 3 days and it does work pretty damn good.