Your calorie needs are based on your age, current weight and activity level. With your age of 50 yrs, weight of 245 lbs and unclear activity level, which I based at "little to no exercise" since you said you hadn't been walking due to the heat; keeping in mind that calculations are not "exact", I calculated your calorie level at 2068 calories/day to maintain your current weight (I did not use the MH calculator).
In order to lose weight, you would need to drop to 1968 calories/day. This does not take your medical condition into consideration, as there are conditions that can actually cause weight gain/inability to lose, in which case, the underlying problem would need to be addressed first (i.e hypothyroidism, insulin resistance, etc)
It's generally recommended that you eliminate as many processed foods as you can; these would include foods made with processed (table) sugar, white flour, rice, regular pasta, etc. The closer to raw your food is, the better; if you shop around the outside perimeter of your grocery store, you will usually be getting the healthiest foods; the closer you get to the center of the store, the more processed the foods will be.
For most people, a diet of consisting of lean proteins, whole grains, low/no fat dairy, lots of fresh/frozen veggies and whole fruit, along with "good" fats from foods such as avocados, olive oil, nuts, seeds, etc; along with controlling portion sizes, works quite well.
Maybe if you can't walk, because of the heat, you could find some other low impact exercise to do inside; or perhaps there's a mall you could go to walk in air conditioning.
Since you have medical issues, any diet or exercise routine should be approved by your doctor.
Your medical situation is unclear but alot of the base things with weight gain is the metobolic rate and the hypoglycemic index portions of your diet intake on the foods involved with your diet.
A base plan that can help you is high protein - low carb - no flours /sugars including fruit juices and eating a high green diet loaded in antioxidants. This "can flush the system into high gear and burn calories better for you to be able to take in the needed calories daily to keep the body in high gear.
Again without knowing the history of your medical situation much more can't be brainstormed but know that this could be a good reason why you are still at this weight and not able to take it off.
Menopause is a toughy too when that comes upon us and usually a depletion in the way we utilize our minerals and vitamins can change inside us. A simple few tests done can tell you if you are depleted in lets say - Vit B with actually melts the fat into more liquid form to burn away and menopause if this depletion is there can harden it to make it tougher to get off. Another is the hard mineral base like iodine and magnesium that have subsiquent metobolism effects and as we now our metobolism changes as we age so those 2 components can be helpful getting things back on track too.
Slow digestion and even adding in acidophillus can help get things rolling to - waste build up is common with slow metobolism and again as we age that can cause us to slow down and gain where we didn't before.
Lots of things for sure.. Finding it is tough but it can be done.