I found it best to take my temp on waking.... before moving. My hubby would wake me and pop the thermometer in my mouth and then go down to make me a cuppa tea. I was only ovulating 2-3 times a year because of Endometriosis. I did basal readings with absolute consistency for 11 months combined with 2 procedures to help clear the blockages ("you'll feel a little bit of pressure" *lol*) and was about to go to the next step when I found out I was pregnant (3 1/2 years after first beginning to try to conceive).
If you're consistent with your basal readings and you chart the results every day, you'll see a very clear pattern and you'll become familiar with your body rhythms.
http://www.fertilityplus.org/faq/bbt/bbtfaq.html
This site has a lot of information on basal readings as well as a chart. There are also over the counter ovulation kits you can buy but since I was infertile in the dark ages (18 years ago) I don't know much about them.
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Just to add my own story to this topic.
Began trying to conceive ... after 1 year I went to my doctor... 6 months later to an infertility specialist. Went through a number of tests and was diagnosed. Began charting my basal readings and the Dr. did a dye assessment of my tubes which he said often clears the way in cases that weren't too severe. Six months later he performed the same procedure as well as a surgical procedure to clear the worst of the blockages. At my assessment 5 months later, he explained that the fibrous blockages had returned and since I hadn't become pregnant, chances were good I'd need IVF.
My husband and I decided to give ourselves a year to save and relax without even thinking about pregnancy since we wouldn't be able to do it until we could afford the IVF. 3 months later I had a summer stomach flu that lasted a few weeks *lol*.... it didn't even occur to me that I could be pregant because the doctor had explained that I was worse than ever.
I was 3 months pregnant when I found out and my son is now 18. My specialist assessed me again a year after our son was born and let me know how lucky I was that I'd conceived because my tubes were severely blocked and conception would be next to impossible.
When our son was 5 he asked for a little brother for Christmas... he told us in November that it was all he wanted and I went out and bought books about being an only child so I could explain to him how special he was and why we couldn't give him a brother. He was very sad on Christmas day because no matter what we said, he wanted a brother.
Two days after Christmas I was feeling odd. I had the most bizarre feeling and I felt foolish even mentioning it but the feeling persisted the next day so I bought a pregnancy test without telling anyone. "Next to impossible" was born 7 months later and will soon be 13. :)
