It seems like we have lots of bf moms on this thread. I'm trying my absolute best to bf, especially since I have a preemie, but I have 2 major challenges. First, my baby isn't with me

I have limited chances to put her to breast as I'm not producing much and she gets too tired to take her bottle. I don't want her to get an ng tube because I don't know what I'm doing or I don't have milk. Second, I had a breast reduction 15 years ago, it was pretty radical, the removed and reattached my nipples. But I healed well, got sensation back right away, and it was a long time ago.
I still don't have much supply on day 6, about 15 ml a day that I painstakingly pump. But tonight I'm getting strong cramps, my bb ache and are very firm. Is tis a sign of milk coming in?