It's a pleasure, Jasmin. You may not absorb as well as I do, but I'm sure you know standard advice is to wait 3 months for the body to adapt to any new HRT product/regimen unless you're sure it's clearly wrong for you or side effects are intolerable. As a migraineur I do find changes in HRT can cause headaches, though these have not been severe, always settled after a while & I've thankfully not had a return to full blown migraine since final period nearly 9 years ago. Even starting Vagifem as my first experience of HRT several yrs postmeno gave me daily headaches in the initial loading fortnight. Mary G's posts show she's another lady who's very sensitive to changes in oestrogen levels (as regards migraine response). It's definitely not all in our heads!
I couldn't get my GP to test oestradiol either - I get mine done privately & if you're not long on 75mcg, perhaps a bit soon for a good indication of what sort of levels you'll get on average? There's some fluctuation over the life of each patch too.
If you feel the 75mcg is really not right for you, you could maybe try cutting your next patch by a third to take you down to approx 50mcg & see whether that feels better? They are matrix patches so you should still get even release of oestradiol from a part patch. Then, if the headaches & irritability go but you still feel you really need a higher dose for symptom relief, you could go back up a bit by increasing patch size gradually. Estradot are so tiny I actually measure mine with a ruler if I need to cut them down!