Basal temp options

So, i have been orally taking my temp every morning before i get up since December to try tracking my ovulation. One of my friends recommended me try doing this bc she has had good luck getting pregnant using it. Well i have noticed my temps are really low compared to what to told me they should be. Some months the highest temp i see is 97.6. Well i read an article that if you are a mouth breather then that can lower them also. So i started thinking next month i would try vaginally, but i use a regular thermometer that you would use when you are sick. We happened to have one that was never opened so i snagged it and keep it on my bedside table. I feel a little weird thinking about sticking a thermometer in my vagina so i was wondering if anyone had any experience with this?! Any tips for us? We stopped all birth controls in October and i started tracking my temps in December but yet every month aunt flow shows up and somehow we miss the mark. Any help would be so greatly appreciated!