Hello & welcome,
As you have already finished your course of Antibiotics, then it is advisable to wait & watch a couple of days to get ulcers resolved.
In mean time, you can apply topical
anesthetic gel or ointment or use any anesthetic mouth wash to get instant but short term relief from pain caused by ulcers.
Nausea that you are experiencing is of more concerned as it may be caused by irritation of
gastric mucosa associated with the use of Antibiotics.
For this, you can take antacid drugs for short period.
Avoid spicy foods as it not only will increase nausea but also hamper healing of the ulcers. Increase intake of food which is light to digest.
Drink plenty of water to avoid fatigue &
dehydration.
Ulcers & Nausea may occur after Antibiotics use due to gastric irritation followed by
vitamin B12 deficiency which can be treated by taking
multivitamin drugs but after examination by your physician.
Take care.