Hello and hope you are doing well.
On exposure to the allergen, an Immunologic (IgE) or a non-immunologic reaction is set in process, which ultimately releases histamine, which acts at the peripheral receptors, resulting in allergic reactions and rashes.
The aim of the therapy is identification and removal of trigger factor. It is the most important and the only effective long-term therapy. Since you are already aware of the triggering factors, avoid the same.
Antihistamines block the histamine receptors and prevent histamine from acting and thus help in preventing rashes. So, take Antihistamines to counter the allergic reactions.
Hope this helped and do keep us posted.
caffeine is a stimulant.
your heart racing away IS the cause of your headaches. you are probably very sensitive to caffeine. you should simply cut down the amount of coffee you take. if you really need one, drink just a few sips of coffee.
if you 'accidentally' take some coffee, you can only hang in there. simply drink lots of water. the half-life of caffeine is about 5 hours. so it needs about that much time for you to feel better.
it is not a laxative but a diuretic - i.e. it causes you to pee more often.
FYI, decaf coffee is NOT caffeine free. it is just much much lower in concentration.