A very good question! I increased from three pumps to four a couple of weeks ago and have since had mild almost sinus feeling headaches. But its so difficult - maybe its the vaccine, which I had three weeks ago, maybe its a bit of hayfever, maybe my head is cold from all these nasty winds. Also occasionally I can get a headache with caffeine and I have to back off. I think what I mean is its difficult to pinpoint the cause.
So in answer to your question I am not sure, it could be the extra oestrogen but maybe not? I feel I would like to give it a bit more time before I make any decision re reducing my dose again. It's very tempting to chop and change but then we will never know whether if we had just given it chance to settle everything would have been ok!
How severe is your headache? I would give mine only a two out of ten so its not affecting my life, its just irritating. If yours is much worse then I can see you want a definitive answer sooner rather than later.