Congratulations, Katie.
The traditional recommendations are,
- low impact cardio
- no collision sports
- moderate-high reps and moderate-low weights in weight training
These are basically all because a big momentary strain can cause a miscarriage, as happens for example in car crashes and heavy falls. I don't know of any cases where a woman actually did lift heavy and then miscarried, but that is the general thought.
In the third trimester avoid any exercise where you lie on your back, the womb impacts on an important blood vessel. Ab and core work becomes a problem then if you are among the third of women who experience an abdominal muscle split, diastasis recti. If so, you would have to avoid all compound exercises.
So now is not the time to start a Bill Starr 5x5 programme, or do 20 rep breathing squats. But most hold that 10+ reps, not to failure, will be fine, at least in the first two trimesters. As with everything, being fitter and stronger always helps your health and progress through stressful things like pregnancy.
I wouldn't be taking any "fat burner" supps now, those are mostly caffeine which doesn't help. The effects of creatine supps during pregnancy are unknown, you don't want to be the guinea pig I imagine.
That's the general guidelines given out, but really see an ob-gyn. Get a woman, they're more sensible, the males are all "oh noes you had a sip of wine once during pregnancy and didn't take folate every single day your baby will be a MUTANT!"