welcome to hcm, I really appreciate your concern, No amoxycillin cant cause olfactory hallucinations, olfactory hallucinations it must be tested whether there is any loss of smelling function outside of these episodes. If there is accompanying persistent loss of sense of smell brain imaging scheduling, preferrably MRI, is recommended to exclude tumors. Also it should be checked for upper airway infections like sinusitis which can distort smelling function. If those have resulted normal then it is possible for psychological factors to be the cause. As for treatment, it depends also on how frequent they are and how much they affect his quality of life. If they are not frequent no treatment is preferred to taking daily medications with potential side effects. If treatment is chosen it ranges from local treatment with nasal drops of saline or oxymetazoline several times a day, to medication such as anticonvulsants (Gabapentine) or antidepressants. Please let me know if you have any questions, thanks.regards.