Hi Amykins,
Congrats on your weight loss success and your new bike. This forum is very helpful for new riders!
I am not familiar with Apollo bikes, but it looks to be very nice! I think locking the front suspension for paved paths/roads will definitely improve your ride. Your bike looks very similar to the first hybrid I started on (although I didn't have the option to lock the suspension). My bike was very heavy and made climbing hills pretty tough.
When I first started riding, I fatigued very easily. Seemingly gentle hills turned in Mt Everest for me. That definitely improved over time as I grew stronger and also learned to ride the bike properly (I tended to shift gears at the wrong time, used the wrong gear,etc)
Low carb diets are tricky with exercise. You need energy to get through exercise. Perhaps you should chat with your dr. or nutrionist on how best to fuel up for a ride while sticking to your current program. Be sure to drink lots of fluids too while you ride....it is easy to dehyrdate quickly and that is no fun.
Enjoy your riding, and don't worry, you will improve with each ride!