Is it normal to get piles in the 3rd trimester?

Common. During the third trimester, women have increased urinary frequency due in part from pressure of the uterus/baby on the bladder. While they are trying to get the last minute tasks accomplished, this is "inconvenient" and many deal with this by cutting back on their fluid intake. Frequent urination is much less inconvenient than constipation and hemorrhoidal flares, drink more fluids!
Yes. Many women get piles or hemorrhoids in pregnancy. It is important not to become constipated, so increase your fiber (metamucil), increase your water intake, avoid sitting and pushing on the toilet and take a short walk after meals if it is ok with your provider. If you have severe pain or heavy bleeding from the hemorrhoid (pile), call your doctor/cnm right away.