Sentence examples for only three months from inspiring English sources

"only three months" is grammatically correct and can be used in written English.
It is typically used as a phrase in a sentence to indicate a specific amount of time or duration and to emphasize its brevity or significance. Example: "I have been working at this company for only three months, but I have already learned so much." "I have been studying Spanish for only three months, and I can already hold basic conversations." "I will be traveling for only three months, so I need to make the most of my time."