I'm sorry for the delay, but your question just showed up here now.
Loose droppings can be a sign of stress, and mating is a stress.
Diet can have a lot to do with how a bird handles stress.
Compare what your bird has been eating to the diet recommended by professional aviary keepers: 70% high quality pelleted parakeet or budgie food, such as those made by Harrison's, Lafeber, or other reputable manufacturers, 20% dark leafy greens like kale, spinach, Swiss chard, cilantro, collard, turnip or beet greens, cooked sweet potato, squash, or pumpkin, carrots with the tops attached, dried chili pepper, yellow, green and red fresh peppers, and only 10% or less, seeds and nut foods. Lettuce is practically all water and is of no food value in the diet, and shouldn't be fed to birds. Fruit is okay as an occasional treat, but also contains 90% water and fills the bird up with out providing many nutrients by weight. Grit is no longer considered necessary to the healthy upkeep of pet birds, and can actually be the cause of fatal impactions of the digestive system. Most pet birds' diets consist of far too many seeds and nuts, which are out of balance in calcium and phosphorus, too high in fat, and low in iodine and this imbalance eventually catches up with them. Sunflower seeds are especially high in fat content. Beside all this, pet bird food is usually not shelf dated, and is often more than a year old when purchased. Most, or all, of the perishable nutrients are gone by the time the birds actually eat it. Seeds and nuts tend to go rancid in time, and birds will usually refuse to eat the rancid foods when this occurs, picking the rancid seeds out of a mix. Vitamin deficiencies can result from rancid seed. Check your bird food package to see if there is a "Best by" date printed on the label. You can tell a lot about the manufacturer by whether or not they date their product.
Proper nutrients in balance with one another help prevent respiratory, nerve, skin, feather and organ problems, as well as behavior problems like self mutilation, excessive vocalization, aggression and excessive egg laying in females.The reason for this is that diets high in seed and nut foods tend to cause the liver to become sick, as fat tissue replaces healthy liver tissue.The bird's resistance to both stress and infection is severely lowered when their nutritional state is not optimal. The fiber content of dark leafy greens is extremely important in maintaining intestinal health.
I hope this information is not something you already knew, but I think you deserve a thorough answer as to what may be happening to your pet.
If you should have further questions, please feel free to ask.