Wanted to keep this as a little secret to myself but I want others to also know it soo.
How to Heal Infinitely (Glitch)
Take any item which will be picked up by the player regardless of what you are currently holding (like guns, a sledgehammer, etc).
Drop the item, upon dropping the item, equip the syringe.
When using the syringe, when your character presses just all the way down on the syringe , equip the item again to make the player equip the item you have dropped, you will gain HP and stamina but you should still have your syringe.