Hi, Sheldon, from what I remember, your prenatal DNA test from Ravgen said the father is your boyfriend; that he got positively identified. Are you saying you had a recent miscarriage or birth from this boyfriend, and immediately got pregnant again, and wonder if the second pregnancy is from the other guy but that the test only picked up DNA from the earlier pregnancy?
First, did you have a recent miscarriage or birth (with your boyfriend the father) before you got pregnant this time? In the scenario you just proposed, with the wrong guy the father, how do you explain away the fact that the testing lab didn't find the wrong guy's DNA? (Why would the DNA from the present pregnancy not show up?)
If it "would of picked up old DNA from when I was pregnant with my boyfriend" -- that would be unlikely because the baby was long gone, and if anything is left in your bloodstream it would be just bare traces, if that.
"and so they couldn’t detect the new DNA from the guy I cheated [with]" -- if a test is good enough to detect old traces from a miscarriage (and nobody is saying it is), how could it not detect a great deal more current DNA from a current pregnancy that is in your body right now? There is no logic to this link in your reasoning chain.
"and that it could of gave me a false positive" -- but where would be the positive for the guy who is the present father of the current pregnancy, in this scenario? It's not like a DNA test looks at one marker and tells you who the dad is. It looks for 23 pairs, and can tell if there are markers from more than one dad in the bloodstream.
Sheldon, you should rethink what is the real cause of your anxiety. As I often tell women who are obsessing in the face of medical evidence, identify the real root of your anxiety (I can guarantee you that deep down, it's not worry about who is the dad), and work on that., and the straw-man issue of paternity will die away.