Suggest Diet And Treatment During Second Pregnancy

I have twin two year olds and am pregnant again but this time with just one baby. With the twins I was given so many restrictions from the start I m lost with what to do with this pregnancy because I ve basically been told nothing. My biggest questions are about exercise and lifting. I worked out moderately 3 times a week prior to pregnancy. At what intensity can I continue to work out and is weight lifting acceptable? At what point is it not safe to sleep on my back or do exercises on my back like sit ups? My twins weight about 30 pounds it and often like to be picked up and carried at the same time. Is there a point in my pregnancy when I ll need to avoid this? Finally, is it safe to have oral sex or orgasm during pregnancy?