Hi Haleigh,
I'm so sorry that you are having this problem. Definitely show your doctor this thread but make her promise that she will read the whole thing. ; )
I have the same problem as you do. I don't have UC, IBS, or blood in the stool. However, I have to stop multiple times during any run over about 3 miles and sometimes even on shorter runs. Today, I ran 14 miles and had to stop 5x. I don't appear to have any illness causing me to "go" but my problem is exacerbated by pelvic floor damage from childbirth which has left my rectal sphincters separated. I've tried many things to eliminate/cope with the diarrhea on my runs. My sister (OB/Gyn) and her husband (cardiologist) recommended taking an immodium the night before as well as the morning of my long runs. I started with 1/2 a pill each time and moved up from there to one pill each time. This works most of the time, but it I eat a lot of soluble fiber/acid in the days before a run, I have to stop more.
I do think that a lot of my problem is emotional - I worry that I'll need to go and that makes me go. It does help to take the immodium and eat a lot more insoluble fiber (to bulk up the stools to slow them down). Therefore, I would not discount the prozac option. It may not help you but might be worth a try.
Also, think about creating a pre-run routine that you follow without fail. My pre-race meal is steel-cut oats with soymilk and brown sugar and I find that eating this every time (2+ hrs pre-race) helps give me peace of mind which helps me not have to go during a race. It doesn't always work but seems to help. Something different might work for you (peanut butter waffles, PB&J, granola with yogurt, chicken sandwich, etc) but you want something low fat with low/no soluble fiber that also has some protein to stick with you for your race.
I've run with Depends and they work fine. However, be sure to lube yourself up with bodyglide or vasaline because they will chafe when you start sweating. And, bring a plastic bag and change of clothes (maybe some wet wipes) so you can clean up if you do have an accident. I routinely pack wipes for all long runs, just in case.
I hope that you and your mom and your doctors are able to give you back your runs.
[[hugs]]
Steph