If you are really concerned, i'd talk with you doctor. Sometimes post-partum depression doesn't happen right away and it's not always obvious as to what it is. Postpartum depression can manifest at anytime during the 1st year and sometimes during the 2nd year. It can be very mild to very severe. Your doctor can recommend a thearpist to at least talk to you. You don't have to "feel" depressed to have it. Weepiness is a sympton of PPD.
And I do think that once you have little ones yourself you become more aware of "the emotion of Life". You subconciously (consciously too) have the knowledge of how lucky we are to have children--sometimes i think it's the brain trying to remind us of the pain/trouble we go through to get them. I could be watching the news about a child that somethings happened to and find a lump welling up.
If you have drastically changed your social outings with friends, you could be reacting to not having that, especially if it was something you really found energy from. Even though children can be wonderful, we still need those adult times.
You might think it's for no reason, but look at what you were just doing or thinking, our minds have funny ways of connecting things sometimes and doing one action might remind us of another w/o realizing it. Maybe you feeling a little overwhelmed at the moment. Take a deep breath, relax. Good luck.