Hello and welcome to HCM,
Looking at your professional history of being a refree, it is quite possible that you may have injured your knee while running , bending or performing similar activity.
Inflammation of the joint surfaces can lead to effusion or collection of fluid in joint spaces.
Thus, the pain, swelling and restricted movement of the knee joint can be due to inflammatory process.
Secondly the pain in calf can be due to
deep vein thrombosis (DVT) as you have mentioned.
The incidence of DVT is high in people who have to stand for long durations.
DVT leads to pain in the calf region, however, the pain in knee region is not explainable by DVT.
I suggest you to consult an orthopedician for clinical assessment and relevant investigations for definitive diagnosis.
The treatment of effusion in knee joint is primarily conservative and treatment for DVT consists for drugs which inhibit clotting in veins.
Thanks and take care
Dr Shailja Puri