lower back pain.. is this normal??

Monique
I just turned 7 weeks pregnant today. I worked out for about an hour doing some cardio and did the leg press with 30 lb weights. I started to feel some lower back pain later today. Is this a sign of a possible miscarriage or is it normal to have lower back pain? Mind you, I am also constipated, and gassy. Please help! Suggestions are greatly needed!