Unless you have an ultrasound give contradictory information, the doctor will count your pregnancy time period in weeks as beginning on the first day of your last period. He does not think you got pregnant that day, but that is when the medical count of pregnancy begins. So he would say that you are (today, April 27) 4 weeks 4 days gestational age, or 4 weeks 4 days "pregnant." This is NOT counted from conception, as you can see. But it is the way doctors do a count.
Now, you seem to have quite short monthly cycles, if one period came on March 6 and the next came on March 26. This would push your ovulation to rather early in your cycle, like about day 6 or so. It's not impossible, lots of women have short cycles, and the way it works is that you ovulate and then in 14 days a period comes, no matter how long or short your cycles are. If this always happens (and you weren't just irregular in your cycle this one time), you could assume you ovulate around the 6th or 7th day of your cycle. This is not what doctors use when computing things from the averages of lots of women, the assumption they would make is that someone ovulates on day 14. But it is not unusual for someone to have regular, short cycles. If this is true of you, you probably got pregnant (actual conception) on around April 1 or so. If your reason for asking the doctor "exactly how far along I am" is because you were trying to decide which sex produced the baby, it might be sex as early as March 27 (because sperm can live a few days in your body).
When you get the ultrasound, ask them to give you an estimated due date based ONLY on the developmental markers and crown-to-rump measurement of the embryo, not on assumptions made from counting from the first day of your last period. They might change your "weeks" count based on the baby's measurements. They will measure the baby, work out by its size when it might have been conceived, and then count back two weeks to get to a mythical first day of your last period based on averages, just so your weeks count will calibrate with all the average measurements.
If you need to know for sure when you conceived because it is a question of one guy or another, right now you can assume it was sometime between March 27 and April 4 or 5, and when you get your ultrasound, get from them not a "weeks" count because those are too confusing for this, but an estimated due date (EDD) based only on the embryo's measurements. Tell them your cycles are irregular and you don't want them to put your first day of your last period into the mix when figuring out the due date. Then take the EDD home and plug it into an online conception calculator to determine an estimated conception date. Or just count from the EDD on a calendar back 266 days, to get your estimated conception date.
If all of this seems too hard but you do need to know, once you get your ultrasound and the doctor is reading it, tell the doctor that you would like to know not "how far along" you are or how many weeks "pregnant," but instead when conception was. Use the actual word "conception." This will make it clear in the doctor's mind that no matter what weeks slot he puts you in, you are interested in that specific question.