Dear Mama-
I understand you situation. I would have a serious conversation with Hubby and ask if you could reduce the frequency of the visits, just not stop them altogether (as I know that would be impossible). This is a critical time, for you, for the baby and for your bonding time together. The other part of the conversation you need to have is that you need HIS support for BFing the baby. Tell him you need him to step up and "protect" you and either give you the chance to nurse by excusing yourself from the visitors and going in an alternate location/room or that if he feels this is rude, tell him you will do it there in front of whatever guests are present and they will have to deal. His support will be SO critical in making this a success.
Now, IMO, if you are with your baby, there is no reason you should be pumping. I nurse with company present, I nurse at the mall, I've nursed in a parking lot... If you are doing on demand feeding then this is what you need to do when baby is hungry. There is really no ifs or buts about it. And, you can be discrete about it - use a lightweight blanket or buy a nursing shawl (Target). After a while, baby will know what to go for and where and really, even those are unnecessary (IMO). As an example, I once nursed on the bleachers at a traveling circus we had gone to. The baby was fussing and I just discretely sat him on my lap and did what we needed to. I was a bit nevous until Hubby put an arm around us and reassuringly squeezed my shoulder. Noone said a thing and I am not even sure they knew or noticed.
I produce a huge amount of milk in the beginning and I will either pump off milk between feedings (about 15 minutes after baby finishes) or I will "finish off" whatever baby leaves behind. Sometimes this means feeding a little on each side then pumping each side. Other times it means having to only pump one side. I just make sure that baby starts on the pumped side, if it is not being done equally. It may not seem like alot, but removing even an ounce to two feels better. I am a full-time working Mom and I usually freeze this milk for later use when I return to work. Occassionally, I do need a break and we will use that milk for Daddy to feed the baby, but ultimately, even if not nursing, I pump to maintain the supply.
Fluctuations in milk are typical. This is totally normal so don't worry too much. If you baby seems full and content and is gaining weight, I would not worry too much about these changes. Using the pumping techniques (above) you can help even this out a bit.
I too have experienced "lumps" in the breasts. The best solution I have found is to take a really hot shower and then let Hubby massage them out. I will not lie, for me it hurts like H#LL, but the area is usually too tender for me to touch and rub so I let him do it. I'll usually cry and sob and clench a pillow, but after a few massages two or three times a day, while continuing to nurse, things loosen up and feel better. I have never had to see a doctor (i.e. things have resolved and not gotten worse).
Lastly, your MIL will continue in her ways, unless you create different expectations. If she is entertaining the baby, tell her you are going for a nap and then do it (and set an alarm for 20 or 30 minutes later). If she comes over, ask her to pitch in with dishes or clothes or assisting in preparing dinner, whatever you need. She may not realize that you need the help or she may not want to impose or she may be worried she is doing it "wrong". You won't kow until you ask her to assist. If she is unwilling then make the most of what you are getting - time without baby attached to you - and do something small. Just don't exhaust yourself. If need be, a post-partum doula may be an option that you explore with your husband. (Not wanting to spend money may be exactly what he needs to see to get him to speak up to his Mom about the family's needs....)
The final issue is her insistance that you formula feed. If this is something that is really bothering you, arm yourself with facts (the internet is full of them) about the benefits, share them and then simply state that this is a personal decision and that you appreciate her support in this matter. Honestly, if she is struggling so much over this basic [personal] decision, the future looks to be a long road as you begin to decide on the values and morals you want to instill in your child.
I wish you lots of luck.
~C.