Doesn't sound like an ACL problem from your description. An ACL tear normally requires quite a significant twisting force to be placed on the knee, so it's unlikely that this would have happened without a traumatic injury or accident of some kind. Also one of the main characteristics of an ACL tear is instability, which you don't mention.
Unfortunately your symptoms - discomfort, popping, swelling - are quite general. There are a whole range of things it could be ranging from muscular damage to a meniscus tear, or a subluxation (where the kneecap slides out and in again - this can cause lots of pain and swelling even if it happens very quickly, as it can damage other parts of the joint.) I'd encourage you to get to a doctor for a full checkup if the symptoms persist.