The best person to ask is your instructor. All the advice you'll get on PPRuNe is great from a theory point of view, but frankly we don't fly with you. I have no idea how your hands and feet skills are. I have no idea what your decision making skills are like. Therefore, I have no idea if you should go solo, and neither does anyone else (unless they're your instructor).
[BTW, that comes off a lot harder than I intend it on being.]
Sit down with your instructor. Ask the question. You are paying for the lessons, so you have the right to ask. Find out what errors you are making that prevents your instructor from sending you solo.
Fix those errors and you'll likely be sent solo. If you're not sent solo, then ask to fly with another instructor and get their opinion.
However, only flying 2 1/2 hours per month would not typically be sufficient for you to make the progress required to be sent solo. Remember: going solo is competency based, not time based.
As for your instructor making you complete the upper air work exercises after a 5 month break - that would be normal. I too would want a student away from flying that long to prove to me they remember the basics.
I hope that makes sense.