What about this:
·I need to prepare for the test
·I need to prepare for the test since now
·When you do a Review Exercise, you should start checking all the topics since the beginning.
.When you do a Review Exercise, you should start checking all the topics from the beginning.
Either of these would be acceptable but "from" the beginning would be much more common
.My mom has been sick since Agust
·My mom has been sick from August
these expressions are confusing to me because both choices seem to be correct...but im not really sure