I have a few more doubts on these sentences. Thank you for your help.

1)The bus, by which I usually come to school, was late this morning.
2)The briefcase, which you put on the book-shelf, is Peter's.
3)You'd better/should (put)/If I were you (in your place), I'd put a bandage on your bruise/on it/ on (Are the three alternatives correct?)
I had a headache/stomachacte/toothache/backache (Do you know others?)
4) My stomach hurts/aches, I have a pain in my stomach (belly?). My stomache is sore (???)
5)I had a rash (on my skin). The doctor prescribed antihistamine to me. (but: I was prescribed antihistamine).
5) I'm allergic to cat's hair (??). I sneeze whenever a cat come near me.
6) We stopped at a motorway restaurant for lunch (late in the evening/early in the morning).

3 answers

1 - OK

2 - If there is only one briefcase and you put it on the bookshelf, then this sentence is fine. If there are several briefcases and the only one put on the bookshelf is Peter's, then remove the commas.

3 - yes, all are correct

4 - period after "aches" -- all else is fine

5 - no need for "to me" ("I was prescribed" is incorrect.)

should be "cat's fur" -- also "comes" not "come"

6 - OK
1 is kind of awkward. I would change come to take.
If you change "come" to "take" in #1, be sure to also delete "by."