I haven't started my period in almost 3 months...?

My period used to be regular, like clockwork, but for the last 6 months i've become more ually active and my period has started to go out of its normal pattern. I'm not on the pill but my partner and I have been using protection. It's been 3 months since my last period and I've taken a home pregnancy test which resulted with negatives. These cycle are way out of the norm for me, I don't know what's going on with me and I don't feel any different besides this happening. my diet is the same and all that too. Any feedback or ideas of what is going on with me would be great. Thanks!