Congratulations on the birth of your daughter and for choosing to breastfeed! Such an excellent, healthy way to start for *both* you and your daughter (we all know breastfeeding is wonderful for babies, but did you know it's incredibly healthy for moms too - like a significant 25% reduction in breast cancer? and that the health benefits are even greater the longer you do it?). :)
On to the important topic: the bleeding. I agree with you that it would be *extremely* unlikely that it's a period, especially if you are exclusively breastfeeding (no pacis, no bottles of formula, etc.). So the 2 most common things would be:
1) an increase in your activity, and your body is responding w/ more bleeding as a little reminder that you're still healing, maybe take things a little slower for several more weeks, etc. This is probably the most common reason for an increase in lochia/bleeding.
2) possible retained products of conception (little piece of placenta still in there, for example) - this happened to me, and my experience with it made it pretty obvious something was up. I was passing bright red clots, these were increasing in size as the day and night progressed. I felt no pain or cramping, so at first I thought the bleeding wasn't anything, but clearly something was happening. ALSO, the big indicator for me was that my milk supply took a *drastic* sudden hit/decrease (I, too, was breastfeeding) to the point where I literally had to use some reserved, pumped breastmilk. It turns out that retained placenta can mess with your milk supply (hormones haven't completely shifted over into "postpartum, full-scale milk-making mode"). I ended up having a D&C to remove the retained placenta (got a spinal instead of general anesthesia so that I could continue to breastfeed immediately). As soon as the placenta was removed, like literally within 12 hours of that, a full milk supply returned (thankfully!!!). We're still breastfeeding and I don't take a moment of that for granted because of how close I was to losing that chance.
So... keep an eye on things, be gentle to yourself (even though you might want to be really active) and trust your instincts. If you feel like it's an increase in bleeding due to being overly active, then give yourself some time to rest and see what happens... difficult, I know, with having a newborn and a preschooler since that was my situation too, but try to enlist friends or family or a sitter! If your bleeding doesn't subside, or even if you just feel like something's "not quite right" or if you see other odd signs (like a sudden drop in your milk supply and your baby seeming hungry or frustrated at the breast), go to your care provider and ask them to do a transvaginal ultrasound to determine whether something out-of-the-ordinary is going on.
Hope everything resolves quickly and that nothing at all is wrong, and hold your babies close... my 2nd one (now 16 months) seemed to grow up way faster than my 1st (now 4 yrs old), and I just miss those precious newborn months, and all of those fleeting baby moments! All the best to you and your growing family. :)