It's hard to tell. The greater the HCG concentration in your urine, the darker the test line will be. The control line will be dark no matter what. In early pregnancy, HCG amounts should double every couple days in a healthy pregnancy. In a nonviable pregnancy, they hardly increase at all, and when you are having a miscarriage, they decrease.
If all conditions were exactly the same (impossible to make happen), the line from yesterday should have been significantly darker than the one from last week. However, if you used FMU the first time and tested in the middle of the day yesterday, if you were more hydrated yesterday, or if you waited longer after using the restroom before testing the first time, it is quite possible that you could get two light tests in a row. It could also have to do with variance within the tests.
You could take another test in the next few days and try to keep as many factors the same as one of your other tests and see if anything changes, but when you're using urine-based tests, you can't really rely on the results because they are not accurate enough to make a diagnosis. They are qualitative tests, and many things affect the quality of the line. You can't see if HCG is doubling or not. If you went to see your care provider, s/he would probably recommend serial beta HCG blood tests that would show the exact amount of HCG every couple days so that you could see if the HCG levels are doubling properly, increasing more slowly, decreasing, or staying about the same. That would give you more concrete information, but it would not likely change the outcome of your pregnancy.
You could try to do something similar with home pregnancy tests, taking one under similar conditions every couple days. For many women, watching that second line get darker and darker sets their mind at ease. However, due to the impossibility of keeping conditions the same (including test variance), you are likely to see, in a healthy pregnancy, a gradual progression from light to dark, but a few tests that may seem lighter than the previous test. It is likely that when a test doesn't show up as dark as you were expecting, that would cause unnecessary stress in a healthy pregnancy.
It is up to you to gauge your own stress level and your own need to know. Is it worth taking a few more home pregnancy tests in the hopes that it will ease your mind while risking that it would cause undue stress? Is it worth paying for more objective tests that will tell you exactly what is going on, even if does not change the inevitable? Is it possible to relax in the trust that you will know more eventually, or do you need to know to be at peace?
More hugs. It's hard when you don't know what to feel.