Either case warrants checking your thyroid. Low BBTs are often a sign of hypothyroid which can cause some fertility and pregnancy problems. Excessively high temperatures may indicate hyperthyroid. It can take up to 4-5 days to see the rise, but ideally you see it within 3. If being more consistent, or switching to taking your BBTs vaginally or rectally, doesn t help, you should go to the doctor to have your hormone levels checked out and see what may be causing your anovulation.
Long cycles do, however, reduce opportunities to get pregnant and warrant looking into.
It is also a good idea to have at least one cycle every 3 months, brought on by medication if needed, so that the uterine lining does not become too thick. You are most likely pregnant if your BBTs stay up for 18 or more days after ovulation. It is also common to see a triphasic chart, a second shift sometime during the luteal phase, when pregnancy is achieved. A BBT thermometer is more reliable and more accurate. In glass thermometers, fever ones are only accurate to .2 degrees Fahrenheit.