Should I buy another SIM card?

My phone always goes on searching for signal, and then it's stuck there until I reset it. IPhone 5

Did you mean your current Sim receive poor signal? Yes means, Try another network which one is available in your Area. For choosing your new Sim, Go to a phone shop in town, tell them what you want, they can advise.Before getting your cell phone service provider, Make sure your phone is unlocked and accept that carrier, If it's restricted by other network carrier means, You will need to unlock your phone. For unlocking you can approach your current network provider or else try to buy an unlocking service from any one of the online unlocking service provider like http://www.wickedunlock.com/apple-iphone-5/rs11wp9/ I hope it will be very useful to you.