Is it ok to lose weight while pregnant?

I'll be honest I gained over 50 pounds when I was pregnant with my son, he will be 2 this coming September and I've only managed to lose about 30 or so pounds of my "baby weight". After having my son I was told I have hypothyroidism so I know that's playing a role in my having a hard time losing the weight. I'm not sure because my period has not come this month but I have suspicions that I may be pregnant again. I'm still 25 or more pounds overweight I'm about 145 on a good day and I'm 5'2. I'm not on any crazy diet or super tough workout regimen I've just decided to cut out as many carbs/sugars and processed foods. Eat less red meat more fiber and veges and maybe work out at the gym about an hour a day mostly cardio (walking, elliptical and running) is that ok? Can I still lose weight and be pregnant?