Can I run when I am pregnant?

I have recently started to stretch to start learning yoga and I have become sore in my muscles, and was wondering if I am sore the next day after stretching, is it okay to stretch the next day when I am still sore?

1) When I do a 3-mile or 5-mile run, I run for time and try to finish with nothing in the tank. The closer I get to the end, the more I push myself, because I know I don't need to sustain the effort much longer. When I stop running, I suddenly get very light-headed and dizzy. It never happens while I'm running. I walk briskly while I'm warming down, but that doesn't prevent it. Why does this happen? Is it dangerous?

2)  Sometimes after jogging a while, or cycling a great distance, my head begins to spin and I feel as if I'm going to pass out. Is it normal to have feelings like these, and if so, how intense should these feelings be?

It's been about three months since I worked out regularly. I find that lifting for strength (i.e. 80% of max for 5-8 reps) causes me to feel nauseated about 3/4 through the workout sometimes, so that I can't bring myself to finish. I took a weight training course last semester and was affected the same way every once in a while. I warm up, stretch before and after, breath when I lift, drink plenty of water, take care not to eat 1 hour before working out, skip a day between workouts, don't lift more than I can handle (I reduced the weight from what I ended on in the class to a seemingly suitable weight. I got a 98 in the class incidentally). What's going on?

My trainer is getting annoyed because I am not experiencing soreness. I have been working out now with him and other trainers, three times a week, for three months now. Plus I do 45 minutes of cardio four times a week.

I think it's kind of odd that he bases his progress on how sore his clients are. I was always led to believe that soreness in muscles comes from working newfound muscle groups or aggressive workouts. During our workout I am feeling my muscles being worked and I have lost a number of inches and lbs since I have been working out. It seems to be a large issue with some of the trainers at this gym. I am wondering why! Also he had me doing 420 lbs on my legs. I am not a body builder nor do I want to be. I started to tone up. Advise please!

1) My husband is in an intensive training program to become a firefighter. He trains Monday – Friday. As a consequence, he is sore everyday. I know the best remedy for sore muscles is rest… but he doesn't get any. Is there anything else he can do?

2) I am an avid weightlifter. I want to know how to prevent muscle soreness, or flush out the lactic acid from my system. Thank you.