Hi and welcome to HCM..
I am really sorry to hear this about your problems..
I thank you for posting your query here and I'm definitely going to help you out..
I being a surgeon, we encounter so many such cases day in and day out..
I read your question completely and have understood it well enough..
I will analyze all your points and provide information on how to go about..
1. 30 year old with 4mm Renal Stone is ok.. Not a major problem..
That 4mm stone should come out on its own..
2. You being a diabetic should be little more concerned not to contract
urinary tract infection, Uti..
3. Your problem of passing urine 3 to 4 hours apart is urinary tract infection, Uti..
This symptom of frequency is most commonly seen problem..
4. Foul smelling urine again indicates, Uti...
5. Now, don't worry about the stone. Please do the following as advised..
A. Get urine routine and microscopy
B. Get Urine culture and sensitivity..
C. Drink lot of water around 4 to 5 litre a day..
We will see once we get reports..
Hope this helps you, in case you need further assistance, please let me know.
Take care, God bless..