Extender Tips

So I just started extending monday with the penimaster chrome. Haven’t even been going at my full traction, it’s a real mild stretch for me, but I hold it for 4hours with 15-20 min breaks about every 90 mins. My dick feels really fucking fatigued right now however. Like super sore. The base of my balls too. Am I over doing it. My erect length is about 5inches and I’m only stretching alittle over 4” right now because I wanna take things slow. Unlike alot of guys here I actually went to my urologist to find out safe traction devices are and he said they’re safe, but I’m still afraid of fucking up my unit. Should I cut down to maybe 3 hrs a day until I can do 4 easily, or is it okay to be this sore at the start? Thanks guys