Im going thru menopause and have been doing it too. It so freaks me out. Ive tried everything natural to make it stop. Nothing has worked.
The only medication (not sure there are many other alternatives - check by a search) are beta blockers. You need a doctor's prescription to get beta blockers.
How do you know you have tachycardia? Did a doctor tell you or is this a self-diagnosis? What is your resting HR?
Stuff like this would make it easier for others to come up with experience based information, not to be confused with medical diagnosis.