Magnolia, I am going to infuse this next bit of advice with Dr. Philisms.

No matter how flat you make a pancake. It's got two sides.
We teach people how to treat us.
When you choose the behavior, you choose the consequences.
Anger is nothing more than an outward expression of hurt, fear, and frustration.
You can put feathers on a dog, but that don't make it a chicken.
You can't change what you don't acknowledge.
You teach people how to treat you; by what you allow, what you stop, and what you enforce.

The last bolded "Dr Philism" directly applies to your situation. You need to take some responsibility here, Magnolia. You and your husband have taught your inlaws/his parents that they can have free range of your house (not their house -- you financed it yourselves). You allow them to visit for weeks at a time. And, you don't enforce any boundaries with them that you may have verbally set with them.

You are in graduate school, correct? So, you know as a grad student, you have to set aside 2 hours a night to read and study and write papers. That is the minimum amount of time suggested for most grad students. Since you have a baby and a working husband, I bet you can't find even 2 minutes in your schedule to sit down and study?

So, you have to (no excuses) prioritize your needs, your babies needs, and your husbands needs. Create a calendar. Put it in your kitchen. Literally, write down, the blocks of time YOU NEED to yourself: to study, go shopping, get your hair done, dr. appointments. Create a family schedule. My sister does that for herself, her husband, and their children. She uses different color markers for all 5 of them so show the different school/after school sports schedules, parents' work schedules, etc. and so everyone checks the calendar since its in their kitchen every day.

You need to take back control of your house, and your marriage and create a calendar.
Set the limit to how long your husband's parents can visit. They need to compromise -- they can't stay in your house anymore. They need to pay for a hotel. They have the money. They can afford to do it. They have hijacked your family home from you and your husband because you allowed it, as Dr. Phil would say. So, you need to create a way to retake your home back. Even if your MIL and FIL get pissy, too bad! They cannot overrule your home or your lives anymore. And you need to get your husband onboard with this change. Make him see that a family calendar will give you and him a peace of mind. It's a good communication tool for you and he, and for his parents when they come to visit. They now will have a visual schedule that they can't erase or interfere with. Because you and your husband created it. So, they have no choice but to respect it. It's your home. Your rules.