It sounds like you may be overworking your pelvic floor muscles from the frequent intense ejaculations. I would suggest taking it easy masturbating with your doll or take breaks before you go again. Good luck!
I know the feeling mine is different though. I'm a guy and have learned mental orgasms. I can orgasm for hours on and off. It is addicting. I would have never learned if I found out how powerful it is. Anyways sometimes I have so many my penis does hurt a few days
Do you ever masturbate not using the doll? Do you get the ache if you masturbate not using the doll?
Do you clean your toy? I'm wondering if you're getting an infection from not cleaning it.
For sure though, if it's starting to hurt, that's a sign that something is happening. Either stop doing it so many times a day, or switch your methods to see if it only happens with the doll.
If it lingers, you should see your doctor. If it happens with all methods, you won't have to mention the doll to your doctor.