If it's early enough ultrasound wouldn't show anything. Usually it doesn't until you're around 5+ weeks and for many even this is too early to see much. Depending on your cycle length you would be around 4 weeks or so when it happened, and at that point baby is the size of a period at the end of sentences. Even at 5 weeks baby is the size of a seed and very little would be seen.
Even if they didn't find anything on my pelvic exams that would indicate a misscarriage?
It does sound like a miscarriage. Bleeding coupled with dropping levels would be a clear indicator that is what it going on. Further blood work will be able to confirm if this is the case or not.