I think you are in better shape to be pregnant than I am, and I am pregnant!!
You are already eating well and excersizing normally. You may wish to make taking your supplement a regular thing every day, so you minimize your chances of forgetting a few days at a time. If you plan to nurse your son through your pregnancy, then you don't have to worry about weaning him now, and it wont hurt him to do so. Be forewarned, even if you don't experience nipple pain and sensitivity in the beginning of your pregnancy that things will change in the milk-making department.
(I am currently nursing my two year old and 19 weeks pregnant. For the last month, my breasts have felt very full and nursing wasnt relieving most of the fullness. Then nursing began to hurt. Badly. I didnt realize that my milk would turn to colostrum so early, but it has, and my DD still wants to nurse. I have limited her feedings to a few minutes when they become painful, but plan to nurse her as long as possible, if only for 2 minutes at a time.)
If you are not planning on tandem nursing, or would not want to, you may wish to start the weaning process before or right around the time you start trying. It can take several months to wean a toddler completely, and you will want to do it gradually to make it easier on him.