I'm so sorry you have to deal with chemo, and then the discomfort of constipation on TOP of that! If you drink tea, look for Traditional Medicinals "Smooth Moves". It is a tea with senna in it, which should help get things moving.
Whereas I have never had to deal with chemo, I have had frequent constipation when I didn't eat nearly enough vegetables and fruits and instead ate lots of processed stuff.
Drinking just plain hot water is something that I have done with positive results. Naked Juice Green Machine has some great stuff in it. Though it doesn't retain any fibers from the fruit and vegetables, it does have the other nutrients from it.
Aloe plant is a natural laxative, I understand.
Something you may want to look into is a juicer for while you're undergoing chemo, especially on days where you're really not up to eating. Making green juices, (like with kale, broccoli, apples, mango, pineapple, parsley, and cilantro) will give you some essential nutrients and help get the ick out of you.
Once you're able to eat again, look into getting flaxseed meal and chia seeds which you can add to other foods to help you get a lot of good fiber and omega-3's.
*sources: "Fat, Sick, and Nearly Dead" and "Hungry for Change"-both available on Netflix.