Woo hoo Danni! It's exciting to get 2 lines on any test! lol
The positive means that you are likely to O sometime in the next 24 hours. All tests I've used seem to give different time frames. So, tomorrow could be O day which means your temp rise will be Tuesday.
Off you go - get BD'ing!

*Edited to add - if you are not O'ing until around CD20 or 21 and AF still arrives on CD28, that is only giving you a luteal phase (time from O to AF) of 7 or 8 days which is quite short. Everything I have read says that a LP should be at least 10 days and ultimately 14 days to help your chances of conceiving. Maybe it is worth mentioning to your Dr next time you go (unless you get a BFP this month that is!!) Good Luck.