Have been taking one tablet a week for 3 weeks of methoblastin for psoriasis but since I have been taking them I've been feeling the need to throw up at least twice a day, is this bad?

Side effects such as that should always be reported to your doctor. Pick up the phone and leave the message with whoever answers, even if you can't talk directly to the doctor.

have been taking one tablet a week for 3 weeks of methoblastin for psoriasis but since I have been taking them I've been feeling the need to throw up at least twice a day, is this bad??

Right at the top of the list:

Tell your doctor or pharmacist if you notice any of the following and
They worry you:
• upset stomach, stomach pain,
Vomiting, nausea, loss of appetite

You can also call the issuing pharmacy listed on the container. Here is a package insert on the drug:

Methoblastin (http://www.betterhealth.vic.gov.au/bhcv2/bhcmed.nsf/pages/pfcmetht/$File/pfcmetht.pdf)