Hi. When my oldest daughter turned 12 months old, I became pregnant. I continued to breastfeed for the remainder of the pregnancy without a problem. Although I have to admit it became a bit uncomfortable towards the end w/ the huge belly and all, but never had any problem with the pregnancy itself. I had another perfectly healthy baby girl 9 months later. When my 2nd was 1 1/2, I became pregnant again and continued to breastfeed for the first 3 months and then ended up weaning her gradually just because it was right for all of us.
My doctors also suggested weaning but weren't too concerned as long as I was feeling well, no consistent cramping, etc. I looked up a lot of info online about breastfeeding during pregnancy and seems like its a lot more common than you think - always keeping in mind the health of the new baby...
Good Luck! I'm sure you'll do what's right for you...