first thing is you are pregnant so don t take any medication without prescription because you have another life (fetus) in you every thing you take may effect it.some medications may cause harmful side effects in fetus.second thing you said lesions but did t say what is the lesion according my guess it may be ulcerations.These are called apthous ulcers.apthous are generally caused due to immunodeficiency.normally we have symbiotic bacteria in our mouth but the defence mechanisms in the body does not allow them to dominate you and infect.stress causes immunodeficiency so the symbiotic bacteria dominates us and causes ulcerations.in such type of cases we give bcomplex vitamines orally.apart from that we can put riboflavin tablet under in the mouth.take vit c chewable tablets.apply steroid ointment locally on the lesions so that inflammation reduces and does not cause pain.local anaestetic can also be applies before you eat so that the chewing food will not cause pain and you can good diet which is essential to you and your baby.i need more history to advise you further.hope my suggestion helps you.thank you