There is a reason why doctors recommend that you don't try to get pregnant so soon after having a baby...it can be very tough on your body and tough on the baby (of course this isn't to say that things couldn't turn out completely fine either as plenty of women have done this). I would highly recommend looking into charting just to get a grasp as to how your body is recovering from your last pregnancy & the demands of breastfeeding. In most cases you can really figure out if and when you're ovulating while charting, even if you're breastfeeding and/or still haven't had your first postpartum period. Also, keep in mind that if you're still breastfeeding and you do end up getting pregnant this is extremely taxing on your body.
(Alittle about me: I ended up getting my first pp AF when my DD was 14 weeks old, started charting right after and figured I probably didn't ovulate for the first 3-4 cycles which were each 28-30 days long. I got pregnant again when my DD was just short of 12 months old and I was still breastfeeding her. I am almost positive my supply started to decrease just before I got pregnant but it was almost nothing by the time I stopped breastfeeding at when my DD was 16 months old. During the 4 months that I was pregnant and breastfeeding I was horribly sick and extremely tired all the time...I'm convinced it's because my immune system was so taxed and I couldn't keep up with the nutritional demands of being pregnant and breastfeeding because I had horrible morning sickness. I am now 35 weeks pregnant and while I miss breastfeeding my DD I have much more energy than I did while I was still breastfeeding, even at this stage in my pregnancy.)
Sorry so long but I hope you find peace in whatever decision you make!