I think you are probably just fine and good for you for planning this in a safe way! Sometimes when you start birth control it can throw your hormones off a bit and may take some time to regulate.
You just started birth control 2 months ago so your body is probably still adjusting itself. My Dr recommended waiting 3 months for my body to adjust. Like the above poster said bc can cause a lighter period.
You say you have been on birth control for 2 months. I don't know if you mean pills, or the depo shot, or what??? But if you started birth control pills, and were on them for at least ten days before sex, and you have not missed a pill, then you are not pregnant. The pill and depo shots cause a much lighter period than you would have been used to. Especially after the first month. Its one of the perks. It says you have had a little bleeding...and that is your cycle. And if you used a condom as well.....DONT STRESS.