Am I alergic to my acne meds?

so two days ago I went to the dermotologist and had my acne medication changed from minocyclin to doxycycline. I've only taken it for 2 days (100 mlg 2 times a day) and yesterday I had a pretty bad head ache before taking it, and i became kinda tired. I normally take the 2 tablets at once cause I tend to forget in the morning, but i again had a head ache. I took my 2 tablets around 9-1030 and got a bad head ache and got a little dizzy, and had a ringing in my ear for 10 minutes, and to go along with that every time I drink any type of liquid in 10-15 mins I have a bowel movement (and while on the minocylin I was constapated....all the time) and my heart rate is kinda high for me. am I alergic to the doxycycline or is it just a reaction from taking such a high dose at once? (the doxycylin is also 100 mlg) please let me know, because I am kind of concered