Thanks for sharing your query with us.
As per your disrception the white and purple lesion on roof of mouth can be of ulcers. If it is caused by viral infection it will subsided along with the viral infection treatment.
If it is not a viral origin,it can occur because of side effect of antibiotics or other medication you are taking so I would advice to complete with your medications dose and then again observe.
If it would not heal then you can use mouthwash 2-3 times a day to keep your mouth clean.Take vitamin B capsules ( like Becasule) and apply topical anesthetic
gel like lidocaine
directly to the lesion if it is painful.
Another spots you mentions on your cheeks bilaterally can be normal opening of salivary gland
which is present opposite to molar tooth in every individual and is normal. sometimes they can be seen in fever
. but if it is painful then it could be ulcer.
Red spots at the back of mouth can be normal if it is not painful and not sore or non bleeding.
I hope information provided is helpful to you.
kindly give us feedback.