Noisy breathing is very common finding in the first few months of life..You said that you have visited a paediatrician twice and she has examined him and found nothing..so dont worry..as long as he is able to feed properly.
Next Steps
1)Visit your doctor again..only if the feeding gets hampered or the urine output decrease.2)Meanwhile you can continue the nasal drops which your doctor has prescribed
Health Tips
1) Keep a watch on the feeding and urine output, if that decreases ..then visit your doctor..Take care