my DD did the same thing around this time (reduced BFeeds), but the BF kept going just fine, she is now 19 months.
i wouldn't think cutting back on solids is a good idea if the child shows interest in eating.
BF comes and goes with interest. i have a 19 month old, self directed, similar early weight as yours. early eater of solid foods. followed her cues.
im a beleiver in trusting the process and they are a big part of it, and there are developmental spurts where BF is not as interesting as the rest of their world. dont force it, trust the natural process...
as for constipation, try blueberries, cut of course, very good frozen for teething as well. counter stool softener may be too intense, but keeping the FIBRE (fruit skin peels in tiny bits) in the diet, minimizing blocking foods (cheese, meat, dense breads), eating lots of veggies (peas, avocado, broccoli) helps. keep water bottles available and fluids up.