It's probably due to the sudden rise in weight being lifted. One thing to keep in mind on a cycle is what you were lifting last week before you started and what your able to lift now and then no over due it just becuase you can. If you you can do 10 pounds more today than last week because of the androgens then back it off to 5 pounds more. Your still going to have a great work out and build like crazy. I am NOT in believer in constantly maxing out your weight in each excercise.
You can also keep your weight inrease smaller and increase your volume instead! That's what is widely rec'd while on a cycle. HVT or GVT or Perfect 10 (whatever you call it) is probably the best on cycle regimen that a person can do.
Food for thought.