Can pregnancy decrease milk supply?

[ZoesMommy]

I am 6 weeks postpartum. I began having sex again with my husband about a week and a half to two weeks ago, just before he had his vasectomy. Yesterday, I had some bright red spotting that later turned pink, then brown, then stopped in early afternoon. I have had nothing since.

But my milk supply also seems to have dropped. My son is NEVER satisfied anymore. He usually eats for 20 minutes and if fine for 3-4 hours. Over the last few days, he wants to eat for an hour, and even then, is still not satisfied. Where I could normally pump out 6-8oz of milk, I can now barely get 3 1/2-4oz combined, and my freezer stash is virtually gone.

Is it possible that, if on the slight chance I am pregnant again, that a milk supply can decrease?

[blinka]

I noticed a significant drop in my milk supply immediately after getting pregnant while nursing.  I got pregnant in November and noticed right away.  It was my first sign I was pregnant.  I miscarried, the milk supply went back up.  I got pregnant again and the milk supply decreased significantly again.  I would definetly call your doctor and and ask to get your hcg levels checked.
But as Michelle also said, babies also go through growth spurts where they do nothing but nurse.  I remember at 3 weeks and I think 6 weeks then 3 months as well-can't remember-my daughter went through 48 hrs+ of non stop feeding.  And I mean nonstop.  Constant at the breast.  It is the babies way of building up your milk supply.  If that is what it is one of my lactation consultants said those growth spurts can last up to a week.  If you don't know about it, which a lot of women don't, you think that you aren't supplying enough milk and start supplementing and often give up.  
I highly suggest talking to a lactation consultant and/or your pediatrician to be sure that is what it is or if it is something else.  But make sure to contact your ob to make sure you aren't pregnant.

[Michele, Katy, TX]

I haven't every gotten pregnant while nursing, so I don't know the answer to that question.
It is very normal for the "fullness" to go away some once your body has regulated what the baby is demanding.

But make sure to drink plenty of water.  That is what helps you produce more milk.  Also make sure to continue taking your vitamins and make sure to eat plenty.  Extra calories are really important when breastfeeding.

But also remember that babies will go through growth spurts and all of a sudden want more food.  He may also be using you as a pacifier.  My babies always seem to want to do the same to me.  Infact, they normally start that before I even leave the hospital!!!