Sex while pregnant

So I am sure my paranoia is getting the best of me, but.... About a week and a half ago my husband and I bded and I spotted pink right after. I had an appt. the following week and my OB said that was fine and was normal. So today was the first time we did it since because I was nervous and I didn't spot at all. (It was a different position first time was missionary this time was from behind) now I am worried that since I didn't spot this time, but did last time there is something wrong. I did read that from behind causes less stress on the cervix. I guess I am asking if this has happened to anyone where you have spotted during sex, but only occasionally or when in a certain position lol. Long post, sorry! (First pregnancy... Obviously :)