Probably the quickest way to resolve this is to call your pharmacist and have them check the dose with the doctor (which, frankly, they should've done to begin with). Odds are you'll have your answer within a half hour, at which point you can either resume your therapy or receive the proper dose of amoxicillin.
Dear AIhealth,
Why don't you ask your doctor why he gave you a lower dosage of the drug? Maybe some other tests showed that you are unable to use the normal dosage.
Regarding the dosage yes normal dosage in eradication of H.Pylori is 1000mg (1g) of Amoxicillin combined with 500mg of clarithromycin and PPI in your case Lansoprazole 30 mg - 2 times a day.
Are you allergic to any drugs? For examples penicillins? then maybe your doctor meant to write metronidazole 500mg as there is another type of treatment for penicillin allergic patients which includes metronidazole 500mg + clarithromycin 500mg + PPI.
After the treatment which lasts for 7-14 days depending on the severity of the ulcers, you may again test for Helicobacter Pylori.
In cases when the treatment is not effective, it may be repeated, after a period of not less then a week, and it should be performed with a different antibiotic. However you should consult with your doctor. Hope that the treatment will be effective.
Regards, John.