Hello. Thank you for coming to JustAnswer with your question, and welcome.
It would appear that you have more choices for foods than you realize. For example:
Grains: white bread; pasta; white rice; cereals such as cream of rice, possibly oatmeal (though oats do have some bran and is a whole grain, many people with diverticulitis tolerate this very well).
Fruits: small amounts of melon, apples without peels or applesauce, blueberries
Vegetables: carrots, green beans, cucumbers (remove the seeds), iceberg lettuce, radishes, sweet peppers, squash, onions, celery.
Fruits and vegetables, of course, would need to be limited depending on the amount of potassium they contain, and the amount of potassium you are allowed in your diet. And for diverticulitis you need to avoid anything that has seeds (like raspberries or strawberries).
Dairy: I am not sure why you would need to avoid these altogether. For osteoporosis, dairy foods are ideal for the calcium content. If it is because you can't tolerate them, you might try small amounts of hard cheeses, or yogurt.
For calcium, without dairy in the diet, it would be good to take a supplement. Also, canned salmon or sardines are high in calcium.
It would probably be advisable for you to take a soluble fiber supplement, since it would be difficult to get in enough fiber with a diet low in fruits, vegetables and whole grains.
To sustain energy, you will need to include foods from each group of proteins (eggs, meat, fish, poultry), carbohydrates (processed grains such as breads or pasta, white rice) and fruits and/or vegetables.
Perhaps with your restrictions you are not eating enough calories. So, with dietary restrictions such that you have, you will need to plan your meals, and then keep track of what you are eating to get in enough calories to maintain energy levels.
Here is a link to a site that will tell you how much you need to eat:
Mayo Clinic Healthy Weight Pyramid Tool
Just fill in the information about yourself, and it will give you the calories you need with the amounts of each food group to maintain your health. Also it has a 4 page list of the foods included in each group that you can look at, or print out. Just choose the foods that fit into your diet plan from that list.
You also need to find out what a "low potassium" diet is, according to your doctor. He should give you an amount in milligrams, or "mg". You will be able to keep track of how much potassium you are eating in the foods you choose to maintain this number.
Here is a link to help you do this more easily: CalorieKing.com
This is free to use, and has nutritional information (including the amount of potassium) in almost any food you want to look up, including many brand name products.
You can do this yourself, which will require some patience, persistence and practice. And as I mentioned before, you will need to keep track of everything by doing a food diary. But, the ideal thing would be for you to see a dietitian, which your doctor can refer you to, to make up a detailed plan special to your particular needs.