Regardless of the oil running the machine, physics still apply.
Lack of testosterone is going to certainly effect your ability to build lots of muscle mass, and it will lower your metabolism. It will not however change the simple facts that if you burn more energy than you take in you will lose weight. Now this equation has probably changed a fair bit, and it likely is that you simply need far less calories than you once did, but the basics are still the same.
I honestly haven't noticed such a huge reduction in strength from HRT maybe, 20% or so, but I hadn't really noticed any decrease in stamina. Perhaps some people react differently but, I have increased my exercise a fair bit to prevent from getting too weak. What I mean by too weak is that I don't want to need a man around to do things for me, especially since I am not attracted to men. Maybe opening jars and moving computers isn't exactly competitive cycling but I have managed to remain able to do any real domestic task I needed to do.
I would note that at least for me strength training still works, although it takes more time and effort to get results now, although I am sure my T level isn't 0, since I am taking a fairly small dose of Spironolactone, along with estrogen and Dutasteride. It seemed to me that killing the DHT is more important than T in general. Then again most women don't have 0 T as well.
I think your best bet would be to try and figure out your resting metabolic rate, get a gauge on how many calories your eating, and then figure up a plan that lets you operate at a calories deficit great enough to lose those 7lbs in the time frame you want.
