Hello. It's quite unlikely that you're pregnant. If your period was due to start around the 26th, you had probably already ovulated 12 to 16 days before, and your egg would have no longer been available for fertilization.
The most likely cause of your delayed period was the three-day course of Althea
you took. These pills contain hormones that can, if taken in the latter part of your cycle, delay menstruation
In the unlikely event your period doesn't start within the next week to ten days, take a pregnancy
By the way, if you've been trying unsuccessfully for two years to conceive, it's time for you and your husband to see your doctor about a fertility
I hope that answers your question, and good luck!