DS is 4 weeks old and tandeming is going well so far. DD (almost 3) hasn't increased her nursing too much, which is great. For me, the biggest problem in general with having two is that I find myself pushing DD away in a way that I never did before. I've been very crabby with her and strict. I don't like that. I think the nursing helps a bit because at least I feel like I'm able to give her some love and attention physically, even if I'm feeling grumpy with her inside.
One mistake that I think I've made is that I was saving the full breast for DS to too great of an extent. He's been fussy while nursing, especially in the evenings, over the last week or two and I'm pretty sure now that he is only like that when he's gassy. I was feeding him from the fullest breast or maybe even both, then taking DD up to bed and leaving DS with DH. Then I'd come back down and immediately give him more boobs. I think I was overfeeding him and he was getting too much foremilk because I'd be in a hurry to "tank him up" as DH says prior to DD's bedtime routine and would take him off one breast prematurely to give him the fuller one, causing him to get too much foremilk.
Two nights ago we had a very difficult evening. He must have screamed for an hour (and he really never cries normally). He didn't burp hugely at the end of it, but he did burp and fart somewhat and I am convinced it was all due to gas. So now I am experimenting with always giving him the emptier breast first so that he definitely gets hindmilk, and then switching to the fuller one if he still wants more. And I'm making sure that DD takes the first part of a boob if it has gotten really full. My experiment is only about a day and half on, but so far it's going well. Last night he didn't fuss at all while nursing. Oh, and I'm also trying not to just have him latched on all evening like I had been doing. I've realized that this baby likes to sleep sleep sleep and he gets fussy when he's tired, not just hungry. (DD has never been a big sleeper, so I'm not used to this.) Last night I tried swaddling him after feeding him (instead of just feeding him some more) and DH bounced him on the birth ball for 5 minutes and he was asleep.
So that wasn't really all about tandeming, but it's what's going on with us now.