I got some white rashes inside my mouth and a big pimple on my face. What should I do?

Thrush? The white patches are likely thrush, an overgrowth of candida yeast secondary to the powerful antibiotic (cleocin) you are using. Check with prescribing doctor.
Bumps on face. These types of problems can be due to many different causes. While it is possible that they are related, i sincerely doubt it. Of course as i say frequently it is very good to consult a dermatologist about this unusual difficulty. The same holds for white spots in the mouth.
The rashes inside. Your mouth could be from a fungal or viral infection. Try otc cream for your pimple or u may need antibiotic cream or tablet if it gets worse. See your dr for reassurance. Take care!