The pain in the left side of your abdomen could certainly be the result of a musculoskeletal strain given that you are an otherwise healthy young man who exercises frequently. It is conceivable that you strained a muscle such as the external or internal oblique on the left side of the abdomen either as a result of a new stretching or lifting exercise or an increase in your usual lifting weight. Musculoskeletal strains are often referred to as "sharp" and are usually well-localized to a particular part of the body. They usually get worse with certain movements are are relieved with conservative treatment such as ice/heat, non-steroidal anti-inflammatory medications (such as Ibuprofen), and rest.
However, given that there are other structures in the left side of the abdomen such as the spleen, stomach, and kidney, you should seek out the help of your primary care physician
to make an accurate diagnosis and subsequently come up with an effective treatment plan. Your physician should be able to tell what the underlying problem is based on your history and physical exam alone; further diagnostic testing if needed may include bloodwork and imaging.