first off, stop lying. that's not the responsible way to handle a sexual relationship.
secondly, are you on any medications? have you started on birth control?
thirdly, are you having heavy period-type bleeding? or is it relatively light?
getting your period three times in one month is not healthy or normal. you will need to talk to your gynecologist. if you don't have one yet, go find one (or hit up Planned Parenthood if you're worried about confidentiality http://www.plannedparenthood.org ). your gynecologist can prescribe you treatements for your irregular period. Most likely, it's going to be birth control (which will come in handly since you're sexually active now).
And you will need to tell your doctor that you are sexually active. Don't worry, it's safe and okay to do that. And your doctor will not get mad.
And please, if you haven't done so, make sure to use condoms every time you have sex. The pill is not perfect.
"In God we trust. All others must pay cash..." faw-choon kookie say.