Smoking while pregnant

Hello. I'm new to this app. I'm 30 weeks and 2 days pregnant. I was a smoker before I was pregnant. When I found out I was pregnant I stopped. I picked the habit back up about a month and a half ago and I really want to quit, but it's become a bad habit again. I feel terrible about it. I want my baby to be healthy. My doctor says the baby is developing normally. But of course I haven't told him I've began smoking again (can he tell by my urine samples) I know it's easy for one to say "just STOP" but it isn't. A friend of mine smoked a pack a day her entire pregnancy and her daughter came out fine... Just a little frustrated with myself