Hello, congrats on your pregnancy!!
I am currently 15 weeks pregnant and breastfeeding my 17 month old. It is possible to breastfeed through pregnancy and beyond and it is completely safe to do so.
My cousin breastfed all three children, two through each pregnancy and is still going with the third. So she's been breastfeeding for 4.5 years non-stop!!
I found that my milk supply has dropped a lot since becoming pregnant and now my boy breastfeeds at most 4 times a day. I read that supply increases around the 5th-7th month but it will become more colostrum (still good for toddler) so I'm hoping he will persevere till then as I would really like to continue breastfeeding him till he reaches his 2nd birthday or beyond if he still wants. It will be interesting feeding two by then and apparently it lessens any jealousy for the first child as they will have something in common - mummy's milky!
Another thing to look out for is nipple pain, because of pregnancy hormones nipples are a bit more sensitive. Just make sure your son is latched on properly
Here's a great article on breastfeeding through pregnancy and beyond:
Australian Breastfeeding Association - Breastfeeding Through Pregnancy and Beyond
All the best!!!