I feel pressure behind my knee, very mild pain but pressure is strong no injury. i'm overweight, mostly sedentary, i'm always hydrated, it doesn't hurt much just this pressure. no swelling, no bruising, no redness. not like a cramp is like pulling?

Your complaint can be explained by a range of orthopaedic and vascular conditions. The best way to help you is to have you get the most serious thing ruled out right away, and then the broader list of things can be looked into with less urgency like sprains, strains arthritis or meniscal injuries . Your history creates a concern for a blood clot, get an Ultrasound ASAP for your safety. Then re-ask

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. One possibility is a Baker Cyst, an outpouching of synovial membrane. It would be prudent to see a doctor. Wish you good health!