Where is this drainage coming from?
How old is she?
Your girl has a pretty good urinary tract infection going on. From the sounds of it it may have been going on for a while now to cause symptoms such as weakness. I would highly highly recommend getting her into the emergency vet tonight to have this evaluated and get treatment started. They will probably also want to run bloodwork and take xrays of her abdomen. I would request a special diet that you can force feed her with and that they give her fluids under the skin to keep her welll hydrated.
It is very rare to see blood from a cat that is in heat. If she isn't spayed you could also be looking at a pyometra. A severe life threatening uterine infection. The infection doesn't have to be yellow but blood tinged. And for a bladder infection you would see blood.
You can force feed her baby food / baby meats (no garlic or onion) but this isn't going to take care of the initial problem.
What color are her gums?
Inability to urinate, bloated stomach, high fever, increased respirations, panting, pale or white gums.
Is she howling like she is in eat? Back up onto things and shake her tail? arch her backend up in the air? A cat who is in heat doesn't just stop eating so I believe more is going on.
I believe your next step is to get a rectal temperature on her and I do suggest a trip to the vet tonight if at all possible for you.
Yes, a cat in estrus is menstruating. I am glad that she is eating.