What do you think

I need to know what you guys think its my first time posting on this forum. Me and fiancé aren't trying to have a baby but we also aren't preventing it. We had sex on Jan 27 I spotted little that day like 1 tsp over a 5 hour period, and that was it. A little over 2 weeks later I got my period on the 13th of February. My cycle is 31-35 days, and I bleed for 5-7 days. So February period seemed fine like I wasn'T pregnant. I took a hpt test anyways and it was negative. This month of march I got my period on the 15th but it was only spotting very very lightly that it didn't last all day.  16th and 17th I bled like a regular period and on the 18th nothing it vanished. So I'm confused can you have a period 2 weeks later if you did conceive or is it most likely that I'm not. And why is my period this month so short. I did take hpt tests after my short period and its negative. Would you recommend waiting until April's period to test again?  You see I'm going on a exercise and diet regime that I planned and don't want to harm a baby if I am.  Some symptoms I've had was only in the past week like headaches, I've had vivid dreams that wake me up and can't get back to sleep.  My cat hated me she would love on my fiancé but lately she's taken a liking to me and laying on my belly when I lay down.  I've felt sick on the 24th a feeling of being full after eating a little that I actually puked.  My pelvic area has weird tingling sensation. My lower gut has pressure sensations. I feel like I do feel these things but am I pretending bc I do want to have a baby? I called my ob/gyn office nurse told me to wait until I miss my next period.