Try making a ward that will contain and maintain shield spell for you.
Honestly I don`t know which one do you need but this one might do the trick, and at least according to my beliefs should be standard for anyone who wants to work with magick as it provides with protection in the are that we are constantly at risk at least to a degree.
( https://pbs.twimg.com/media/ByTJQ5zCcAE7mmt.jpg )
That is not really a spell as much as it`s a technique but I can see how it can be useful as well as why you could have energy issues with maintaining it as its a "spell" that is actually meant for short term psychic protection not a long term one like you were using it.
As mentioned before a simplest solution would be to find a strong protection charm that would do the job instead of you, I already mentioned/proposed one but there are many more and finale choice would have to be yours.
As well as charging it for the first time cause if done properly it will maintain itself and its always better to do it yourself.