welcome to the site! I have had Hodgkins twice, white blood count got low a couple times but I didn't have any kind of injection because of it. they just stopped my treatments and let my count build back up. What kind of injection did you get? As far as new pains, just get used to it. Every week there will be something new hurting. sometimes with no explanation. I used to get the common answer from the Doctors, "yep, that sort of thing will happen". Standard answer, I think when they just don't know what else to say. I still have pains of one sort or another. Mostly from the surgery in my neck 4 years ago, and the following radiation that fried my neck. After my first two treatments for cancer I didn't have too many pains. Hopefully yours will go away.
Good luck to you, keep strong and keep fighting, you will be through it before you know it!