You really need to stop stressing out, it is not good to be so stressed during your pregnancy. You have had a lot of women who are really quite intelligent when it comes to reproduction, because we have all been at this for awhile, tell you that it is not possible that it is the guy from April. Even with your scan dates it the guy from march. Your scan dates put conception around mid March, and they will not be off so much that it changes the guy who you conceived with. Those dates aren't off but by a few days. It is not possible that you got a positive test 5 days after you had sex. The embryo wouldn't have even implanted into your uterus at that point. And the hcg doesn't start to produce until the embryo is implanted, but it takes around 2 or 3 days for it to even be enough hcg to show up on a test. It doesn't matter that it was faint at the Dr because anything can affect how dark the line is, like how many times you peed before the test, and how much you had to drink. With everyone telling you the same thing in think you should just rest assured that it's the guy from march. Once the baby comes it won't matter anyway, you will love him or her regardless of who the father is. And if you still question at that point, do a DNA test.