I heard a loud pop in my knee while i was running yesterday it started to hurt and swell up and now the pain has kind of gone away but not all the way?

Hard to say: May be cartialge like meniscus, may be kneecap - the patella, could even be a small fracture. The fact that it is better is good. After this you would want to ice it for 20 minutes 3-4 times today and tomorrow. An evaluation by a knee othopedic surgeon or rheumatologist may have you an answer. You may imaging like X-ray or MRI.