big cramps, little bleeding

Hi! I got the liletta iud about a month ago on the last day of my period. I just got my period yesterday and have had some really severe cramps but not the amount of blood with which that kind of cramping usually corresponds. Could it be that my periods just getting lighter? It seems like it's kind of soon for that.  Also sex got kind of painful last night like external burning. Has anyone had problems like this? I'm going to my doctor tomorrow I hope it's not some kind of infection.