How long has the tank been running?
Are you familiar with the nitrification cycle? If not and also just a great source of information is the Aquarium Advice article - Getting Started linked in my signature.
As for shrimp, they do best in a mature tank. That would be a tank with a thriving beneficial bacteria / BB colony in the filtration media. Stable without fluctuations in ammonia and nitrite spiking, and good maintenance which will help to prevent nitrAtes from getting too high.
A tank which has months of existence because it allows the growth of BB, biofilm and aufwuchs which are little things which colonize and grow in an established aquarium, of which these things are used as foods for shrimps which you might see, pick and clean the aquarium surfaces constantly.
Those foods are important for the health of the shrimp and for teeny tiny babies to forage for the things they need to grow.
You should know what water parameters are needed for the shrimp type which you have. pH, temperature, TDS, kH/GH. No ammonia, no nitrites and kind of lower nitrates.
A planted tank is very useful, or at least one which contains live plants, like aquatic moss, subwassertang, and other lower light tolerating plants, if you are not running a tank set up specifically to focus on keeping a planted tank.
What kind of shrimp do you have right now? There are 2 most commonly kept groups of dwarf shrimp colonies / breeding groups - Neocaridina (like Red or pinkish red Cherry Shrimp) and Caridina (CRS / Crystal Red Shrimp are an example).
How many are there?
and what other companion stock are in the tank?
If you have other fish in the tank they could be considered predators. Shrimp are a normal food source for fish, even small fish.
What food are you feeding them other than spinach or veggies?
Over feeding is a concern in a 3.7G tank.
Do you have a filter? Does it have a sponge covering the water intake?
Shrimp crawl right up into intakes, to feed on all the goody slime that grows in there... and can get sucked up and killed by the impeller in the filter.
There are many companies which produce quality shrimp food.
A nice combo pack comes from Dennerle Shrimp King Food 5 in 1. It seems to offer a great pre packaged assortment of many (5) types of foods for a reasonable price.
They little guys eat a small amount of actual food, so a whole jar of one kind could last you a year of so. My favorite shrimp food company right now is GlasGarten, and Shrimp Fit + is a good overall food. I use at least 4 of their foods, and have tried most of them.
Mosura, Benbachi, and others provide a quality supply of foods for shrimp.
Think of their eye as the amount of food they might eat each day. VERY small amount. And they wouldn't need to eat that every day if you offer an organic blanched spinach leaf or similar (like you do, removed after several hours so it doesn't rot).
They can go for a few days. I personally would do more water changes, and feed every other day. The tiny amounts. The cuttlebone is great too.
