Hi karenja
There are two types of pms really - those who are progesterone intolerant start to get unpleasant side effects as soon as progesterone starts to rise after ovulation - in the second half of the menstrual cycle.
While most of us experience some effects of progesterone at this time - perhaps tiredness, a bit of bloating maybe, perhaps some sugar cravings etc - for those who are intolerant the side effects can be much worse and include headaches, fuzzy/foggy head, fatigue rather than tiredness, and very low mood.
Those who are generally OK during the progesterone phase, maybe suffer from pmt when the progesterone (and oestrogen) levels drop dramatically just before the period - and sometimes when they rise just after ovulation. I talked about this on another thread today - that this is probably due to physiological changes and leads to headaches, tension, irritability - that many of us are familiar with! This dispappears once the period starts - or at least after a few days. I remember feeling the tension drop away as the progesterone cleared from the system, and my head would clear. It was such a relief!
If you are getting headaches during the whole of the progestogen phase then it could be that you are intolerant to this progestogen as has been said already. As others have said these side effects may disappear as your body gets used to this new hormone, which is why 2-3 months is suggested.
Some women feel nausea when oestrogen levels increase rapidly but this should settle hopefully!
I hope I'm not repeating myself too much or what everyone else has already said! Also that your headache clears up - a persistent headache can be debilitating.
Hurdity x