I would probably wait a few days before testing again. How many periods have you had since giving birth, or was that your first? It is not unusual for your cycle to change either temporarily or permanently after having a child, and realistically it is only a few days out from your pre-pregnancy cycles.
The no control line is weird, and not something I have ever had happen - regardless of the test result. If there is no control line, then the result is unreliable either way I would suggest.
Give it time, either your period will come or you will be in a better position to get a definitive result from the test.