M.R.
I would have my doctor check the infection--medication would be faster (or do you have a reason for NOT using medication?) and it could be a different kind of infection. If you are still having intercourse that could cause the spotting/bleeding combined with an infection. I never had implantation bleeding and if your cycles are irregular, you might not even be late. I had some cycle issues last fall and was missing cycles altogether (going six weeks with nothing) or having very heavy bleeding for several weeks at a time. If you don't get a regular period, I would definitely re-test in a few days (I'm an over-tester!), but you'll clear up much faster if you get to the doctor for your infection. Yogurt is great for helping your body NOT get infections, but I don't know how well it works to treat them.