Constipation TMI

I'm used to having a bowel movement at least once a day and ever since I became vegan it's a quick bowl movement too. Barely any push and I'm done but ever since my husband and I started trying to conceive I haven't had a bowel movement which is just 2 weeks until today. Well I just had one and I actually had to push and it hurt. Then when I checked it was 1/3 of my normal. Does anyone know if this is normal while trying to conceive? I don't feel stressed but I did start taking prenatals and I don't know if maybe that is causing me to have problems or not.