Can Itchy, Dry Swelling On Calf Be A Blood Clot?

for the last 6 days the back outside of left calf itchy, dry, skinfeels thick, swollen... back of knee swollen (same leg). thought it was poison ivy / oak... wondering if it could be a blood clot - how do you tell the difference? although, it's itchy - there are not a lot of watery blisters? Any thoughts? Male good shape 5'7'' 185 lbs 50yrs old