Have you taken any replenishing/rehydration drinks for the gastroenteritis you are recovering from?
Things like Dioralyte over the counter might help.
Could you do an internet search and find out if there is an easy way to rebalance your sodium?
I've only recently learned, what lots of other knew, that there is a lot of science around hydration/re-hydration.
For instance DD2 often get an upset tummy before marathons, nothing like gastroenteritis, that affect her sodium levels. She also has to watch her sodium levels while running.
Apparently she is a "salty" runner and has some complex recovery drinks. Her running pal is a "sweet" runner and has a different mix for her recovery drinks.
I hope your recovery is going well and that you find a solution to your low sodium levels.