Ok, it sounds to me like the cough is the same as we have at the moment. It sounds rattly in the chest, there is a little bit of phlem, but it is a rather irritating cough and can be painful in the chest.
Being winter, and with temperatures low and the air dry, this type of cough is caused by the cold dry air. Keeping inside and rugged up with heaters going is fine, except for one thing- the heaters are going to be drying the air out even more, which will cause the cough to become worse.
The respiratory system requires a certain amount of moisture in the air to function normally. if the air is too dry, then the bronchial tubs will be drier too. if they are dry, then an irritation cough will occur, which will be like what RB has. You may notice that in the bathroom, particularly after a shower, his cough will be less. This would be because the air is more humid, and the lungs and bronchials aren't having to work as hard.
To help with the cough during the winter months, a room humidifier or vapouriser will help. It adds humidity to the air which reduces the irritation to the bronchial tubes and lungs, reducing the need to cough. If you aren't able to purchase a humidifier/vapouriser, then a large bowl of water on the opposite side of the room to the heater will help, but not cold - make sure the water is quite warm when you put it into the bowl so the process of evaporation is quicker. naturally, you need to keep it out of RB's reach.
A decongestant isn't going to work, even if you could get it into him, as there won't be anything much for him to cough up. What little he does cough up will be what is produced as a result of the irritation of the dry air. Sounds strange, but the last 18 months, I've really paid attention to our girls coughs, and my own as well. The colder and drier the air, the worse it is, also, if the heater is going, I cough more too.
Not being able to get fluids into him is a concern, but get some hydra lyte sticks and see if they work. Not eating can be just a phase, which all kids go through, so don't stress too much, he will eat when he's ready. If you are concerned about the lack of food, then chocolate might help to stimulate his appetite, and will give him some energy too.
The temperature could mean he has a mild infection. Kids get fevers all the time, and it is a very good indicator of how well their immune systems are working. The fact it keeps going up and down would suggest RB's immune system is very good, so try not to stress about it.
Taking him to the doctor all the time isn't going to help. His symptoms are season related, and there is nothing a doctor can do about the seasons - trust me, I've already asked! LOL
When the weather starts to warm up, the cough should go and he should come back to normal. Just try and keep life as normal as possible, as a change in routine just because he is sick can cause behavioural problems when he's over it - apparently I was rather terrible to deal with once I got better, because I kept expecting special treatment when I was better and would try to get out of chores by pretending to be sick, but honest, it wasn't me
