aha, underactive thyroid messes the whole endo system up!!
the green and herbal teas you mention are not normally associated with strong smells, but a multivit maybe. at certain times of the month, the B vits within the multivit will be used more and at other times, less so. B12 as you will probably know turns your wee strong orange colour and can smell a bit. at some times of the month, your need for B12 will be far greater so less is excreted through the urine, at other times, less needed so more through the wee (and therefore a stronger colour too, does this sound like you?)
It may also be that a time of every womans life is approaching if this problem has only been going on for a while? when other hormones start to wind down, the endocrine system goes into flux (tis why some women suffer terribly at this time). as you also have thyroid trouble, this makes a difficult time more likely (but not assuredly).
have you had a blood test recently?
underactive thyroids should be checked via blood tests regularly, some docs do it once a year (bad idea) others do it 6 months. if you haven't had one for a while, may I suggest you ask for one to be done and see if you can add in a female hormone check too?
keep a diary of food and smell to as that could be helpful if hormones are ruled out.
are you sure the smell comes and goes over the month?
another possibility is a monthly cycle related infection. my notes remind me that I had one lady who had a smelly wee each month for a week (different smell to you though but was a non sweet smell). we worked it out that is was related to her cycle and her immune system/hormones.
I would suggest asking for your blood first for TSH, T4 (tft4), FBC, U+E, LFT, female hormone's and if possible a urine microalbumin test with a GHb test added in for good measure if you have a good GP?