Thanks for the additional information.
Now the first thing that i would think is a simple urinary tract infection. This can cause all of the symptoms which you have been experiencing. A UTI can cause lower abdominal pain as well as back pain, usually that wont radiate don to the legs however it is possible that you have a UTi along with another pathology. Now since you do have burning pain while passing urine as well as throbbing pain, this is the most likely cause. This can be easily diagnosed with the help of a urine routine examination with microscopy and if needed a culture can be done. In addition, since you have back pain i would also like to look into your kidneys, as it is possible that you might have an infection in the kidneys. A simple abdominal ultrasound concentrating on the kidneys, ureters and bladder (KUB) will be helpful here. Treatment is based around antibiotics, which are usually started pending the reports of a urine culture.
Now another possibility is that the pain in your legs and back can be due to back issue, such as a slipped disc / sciatica. This would cause radiation of pain down to the legs along with other symptoms like numbness in the legs as well as difficulty in elevating your legs while you are lying down. This can be easily diagnosed with the help of a xray of the lumbar spine and if needed an MRI of the spine can be done as well. It's possible that you have a back condition along with a co-existing UTI which would explain all of the symptoms.
The swollen legs are a bit concerning as that can be indicative of a number of pathologies, simple UTI or a back problem wouldn't cause swollen legs. It's possible that the swollen feet are due to a kidney issue which could have arisen as a result of the infection. Its important that you get renal function tests as well which would help in determining the function of the kidneys. Secondly the swelling of the feet can be due to a local problem such as varicose veins or even peripheral arterial disease which can cause symptoms like cold feet, pain while walking along with numbness. This can be diagnosed by a clinical examination first of all and if needed a doppler ultrasound of the legs can be done.
Now my suggestion here would be that you contact your doctor and get the following tests done first of all,
1) Urine RE and microscopy
2) urine Culture
3) Abdominal ultrasound (KUB)
If these turn out to be normal, then your doctor can look into the back problem and plan for a xray of the spine as well as a MRI. I hope this answers your query, please feel free to ask any follow up questions.
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