Try the HPT again in another week or two in case it's a timing issue, but those things are fairly sensitive. If you follow directions to the T the next time you take it and it's still negative, I wouldn't worry too much.
Honestly, even on the pill, our hormone levels can vary from month to month. My periods are usually clockwork. Prior to the pill, they came at the same time monthly and were 7 days long. They've been regular since being on the pill but 3 days long instead of 7. However, one month, I had a one-day period. It freaked me out, but I wasn't pregnant. It can honestly just happen sometimes.
Thanks for your comment. The thing that worries me most is I have never had a missed or one day spotting period in my life. I am always right on time and it is always the same. Even why I have taken a pill late or missed it and taken it the next day. I try to take them at the same time everyday but sometimes it is a lot later then others. My doctor won't test me unless I miss my period this month or it is really light again. I did take a home PT that came back negative, but I know so many people who have not gotten a right reading off of them.
As long as you doubled up the next day and took both the missed pill and the pill for that day, you should be fine so long as you have been taking it consistently at the same time daily for over a month. The heavy period was breakthrough bleeding from missing a pill, so not abnormal to see that at all. Some women are more sensitive to having breakthrough bleeding at any missed or late pill than others.
If you feel the one-day period of just spotting is abnormal for you even on birth control, then go buy a home pregnancy test and follow directions. I'm not sure how long it has been since this has happened, but you'll know if it's too early by the instructions.