Pregnancy belly

So I am a heavy girl. I am now 13w 5d and for a while there the lower part of my belly was starting to feel hard. I got sick for a few days and now I'm noticing that it doesn't seem so hard anymore and I am experiencing some light abdominal pain with no bleeding. Do I need to worry of a possible miscarriage or do you all think that I wouldn't be feeling a hard belly yet with not being too far along? Or have any of you experienced this? My fiance thinks that maybe the baby is just moving up.