Bbt question; help?

So, I'm not really sure how bbt is supposed to be if pregnant or not pregnant. This is my first month doing it and I haven't done it consistant enough to post. I'm under the impression that it's supposed to remain high from ovulation through and past when your period is due to get a bfp. I'm late but my bbt did not remain elevated. Only a spike in temp around when I think I ovulated. Is it possible to be pregnant without bbt remaining high? I know many are going to say test, and I will once I buy a test. I'm just not as test happy as some being that I've been ttc for almost 5 years and have come to expect to get my period eventually. I am fairly regular with the exception of being late about 3 times a year which my dr told me means that I probably didn't ovulate that month. Which is to be expected as I am 39. Anyway, my 2 main questions are: Can I still be pregnant if bbt didn't remain high? And can someone give me a little explaination about bbt in general? Thanks ladies!