I had ultrasound on jugulodigastric lymph node that measured 1.8 x 0.8 x 3.6 cm But then I had a ct scan that said "no lymphadenopathy" why is this?

Yes you do. Less than 1.5 cm is by convention not enlarged, assuming CT was done on neck scanning your jugulogastric node area. The question next is how to verify and what to do, best to check with oncologist in your area, and moffitt cancer center is near you, so pls take advantage of these resource to get to the bottom of your concern.