I agree with all the "aboves". My own measurable experience was that my cycling power dropped by some 20% plus my ability with weights also fell.
It's both harder to gain any fitness and easier to lose it in a short space of time. The body seems to have the rather perverse idea that it should be putting on fat and even stealing muscle to convert to fat so that you will be ready for your upcoming pregnancy, groan. Best practice is to exercise and go to the gym frequently, maybe even extend the type of activities you do to include some variety with an activity you didn't participate in before.
Also, if you're over 60, a protein supplement is important. Carbs. and sugars tend to assimilate as fat while protein has a better chance of becoming muscle. I've got some links on this in my bio. and it can help a lot. Initially I had problems with fatigue after say half an hour of cycling but protein helped with that.
Hard to gain in this situation but possible to stop losses at a certain level, hopefully until the testosterone comes back.
Jules