I would tend to agree with you that bodybuilding is the primary culprit for your elevated Glomerular Filtration Rate. Also, if you are supplementing with creatine, that could increase creatinine levels, which would result in a lower eGFR.
I supplement with creatine and lift weights, and I have had a blood test or two that had (mildly) elevated creatinine levels. What I did was before my next blood test, I stopped supplementing creatine for a week with and went a few days without lifting. My results then showed normal creatinine levels.
You could try the same thing to see what kind of results you get.
A couple things that would make me pause though would be your diagnosis of Type 2. I do not know how well your diabetes is controlled. Kidneys are susceptible to the vascular damage caused by diabetes. Combine that with your acknowledgement of always having proteinuria and it would be worth investigating more thoroughly.
How is your blood pressure?