Charting BBT... Wrong!?!? pls help

Stevie • Just tested on 5/8 and I got my BFP. I`m preggo with my first !!!!
I've been charting my BBT daily since 2/15, cycle day 8. It has been average between 97.1 & 97.8 except on 2/21 & 2/24, it elevated to 98.2 both days. I know they say your temp increases after ovulation & remains elevated until your period. I had a + O test thurs & fri. My temp was average those days & then slightly increased to 98.1 on 3/2 & then yest 3/3 was 98.6. I assumed this increase was due to ovulation. This morn 3/4 I temp'd & it's low again, 97.3. 
​I thought temp was to stay elevated after ovulation until period or pregnancy. Now I'm bummed thinking I did something wrong or really didn't ovulate.  Does anyone have this prob? Can anyone provide any insight? 
​I'm getting frustrated & just down bc TTC for a while, nev got a +O test in past & BD'd on the 2 days I did & day after (2/27, 2/28, 3/1). Past couple months AF comes late & plays me thinking I could be preg. Thought I could maybe be preg this time , was feeling hopeful bc BD at correct times & now my BBT isn't consistent with ovulation. 
​Please help!!! :-(