I'm a 23 yr old female why am i having sharp pains in my left knee?

Lots of reasons: There are lots of reasons, possibly a reactivation of an old injury, maybe some transient arthritis, you may have twisted it without knowing it at work, it might be referred pain from your back. Often, in your age, it is due to minor trauma and Ibuprofen helps. Symptoms like these are best evaluated in person by your physician. Based on the findings, a treatment plan can be developed to help you.