Hi there jd - your migraines may be due to ongoing side effects from continuous progesterone, especially re energy/fatigue. Personally I wouldn't put gel on upper arm near breast especially if this is leading to tenderness though the spec does say you can - all the other products patches and gels say lower abdomen. Having said that an increase in systemic oestrogen levels can cause temporary breast tenderness so may have nothing to do with where you applied it.
Another cause of breast tenderness is a natural cycle resuming ie you may not have been post-menopausal despite 12 months without a period? How old are you and how long was it since your last natural period before you started HRT?
Yes if you stopped the utrogestan this can cause spotting or a bleed if there is any lining built up.
If you are getting all those headaches you might prefer to take the utrogestan cyclically and then you will get a predictable bleed and then if you suffer pms then hopefully your headaches/migraines will only be once a month as mine used to be on HRT.
I would sort out your oestrogen and progesterone before thinking about testosterone personally and I can't comment on the effect of T in women who take progesterone continuously. I am still on a cycle in late 60's and take T every day.
Hope you manage to sort it so you feel better soon
Hurdity x