B.G.
Wow! 8-9 sessions is amazing! Well done!
I was faced with a similar situation - pumped exclusively, had a 2 1/2 year old. I was very optimistic at first, but reality set it.
Do what you can, and try not to stress. Pump what you can, within reason, and supplement with formula. No problem.
If you drop a session, your supply will probably drop a little bit. That's just they way it goes, right? I did that. I stayed at 4 to 5 sessions for a couple of months and then switched to 2. I did first thing in the morning and right before bed. I was able to do that for another month or so before I had to admit that I was one grouchy mamma.
I also had to deal with the Mommy Guilt. I really wanted to be able to breast feed my son for at least one year, and I ended up lasting about 4 months! But I saw how much more relaxed I was and how much happier my older son was and realized that this really was what was best for our family.
Do what you can and know that you are an awesome mom!