Several concerns rolled into one here, so I'll try to break them apart in a series of comments.
First, what do you consider symptoms of cystitis? I'm going to make an assumption that you are female, please correct me if you are not.
D-mannose can do ABSOLUTELY NOTHING when taken by mouth. D-mannose is ONLY useful as an internal wash that would require catheterization to diminish bacterial adherence inside the bladder. There was a specific study done to demonstrate that no mannose whatsoever reached the bladder when consumed by mouth no matter the dosage. The only way it might get there by mouth is if you are diabetic.
If you had an old prescription for amoxicillin and you took it, unless it was given by your urologist for the next occurrence of an infection, not a good idea. If it was a leftover and not a whole dosing schedule, not completing your regimen from the originally prescribed treatment is bad. Depending on the infection, treatment might be 3-7 days, but self-medicating with an antibiotic that is too short of a run will cause resistant strains of the bacteria to flourish as a result. Although you were prescribed Cipro, unless you have been tested and PROVEN to have a bacterial infection, taking any antibiotic is a bad choice. The amount of damage Cipro does to your digestive system will require a month of probiotic use afterwards. Do NOT stop taking them now. You have to take the whole course once you start.
There are two tests that should be immediately performed when you think you have an infection. 1) do you have a bacterial infection and what kind of bacteria is it? 2) which antibiotic tested is the one that killed the bacteria found in the culture. If you do not get specific, you end up fostering resistant bacteria, especially when you have recurrent issues with this.
Yes, you are probably over-medicating. Has your urologist made a specific distinction for you between recurrent UTIs and cystitis? They have similar symptoms but are not addressed the same way.
Are you taking any other medications (they might be triggering some of your symptoms)? Do you have any commonly contributing factors like a need to use catheters, are you incontinent, or does this occur more often after sexual intercourse?