GA pilot reported temporary loss of aircraft control when they encountered a downdraft during cruise.

Narrative

I was flying a small aircraft for my first IFR solo cross country. My route was ZZZ1-JAX-ZZZ2 After departing JAX flying as filed at 6000 ft; I was asked to descend down to 4;000. I noticed I would be flying straight into the clouds - which by the looks of them seemed fine. I am an instrument rated pilot and current for IFR flying. I advised Orlando ATC [of] my request to deviate from buildups - they agreed. I deviated and then I requested an altitude change to 3000 to avoid the large build ups.I requested further deviations for weather avoidance several times but I was denied. I found myself in a rain shower which pushed my plane down due to the downdrafts. I was rapidly descending at this point. My airspeed was in the yellow and the aircraft was getting harder to control. While trying to maintain control over the aircraft; I advised ATC my concerns for the safety of flight; requesting an altitude change; I was denied again and advised to fly at 3;000 ft which I flew. I believe if i requested to stay at 6000 when the controllers gave me 4000 initially instead of descending down into the worse weather; I might not have broke[n] aircraft separation.