welcome to HealthcareMagic
If you have taken rat poison a month back i guess you have been treated for that and recovered from poisoning
.The pain in stomach and sudden vomiting
can be due to Gastritis
which may be a problem right now.This can happen as a side effect of the rat poison as well as the treatment you took.So please consult a doctor and get examined and treated.You may need to take antacid
or even Omeprazole
and for vomiting you can take Tablet-Domstal
8mg.But better get examined by your doctor and he will treat you better.