Secrecy with Periods?!!?

Today in my drama class we were performing a play and everything was going fine except for the fact I had cramps. I sat down then during my scene I had to get up and perform it out but I had very bad period cramps. When my female teacher asked what's wrong I told her I was having cramps because I was on my period and my male drama teacher turned around, gave me a look and told me "you shouldn't announce those kind of things" at that point I went off and said "I wasn't announcing it I was simply telling someone why I couldn't perform. What's wrong with that? He turned away and ignored me. I'm so furious about this! Why are people so disgusted with periods?