It could be that you are having false hypos - where because you have been running high for a while bringing your levels down to normal makes you feel hypo, even when you're not.
Gliclazide has side effects of headaches. I don't know, I've never taken it.
Levemir has reported side effects of flu like symptoms. I've never had anything like that on levemir, I would imagine it's pretty rare.
I can completely understand the desire to take control if you are feeling rubbish. But it seems like you are on a fair bit of insulin & your levels still aren't down to normal. Do try and discuss the risks and benefits of medication or no with your doctor so that you can be sure you understand the decision - they might even be able to come up with alternatives (like, literally, an alternative insulin) or just stopping the Gliclazide as you come down to normal levels.