It is totally normal, if you are not sure, just change your activity (laying down - get up and walk; eat; take a shower), if it is braxton hicks, they will stop or change in pattern, and you do not have much to worry about. With each pregnancy your body prepares differently for labor, depending on the individual needs of that particular baby.
Make sure that you stay hydrated, -- do not limit your water intake and salt to taste; dehydration can cause contractions.
Make sure you have at least 100-120 g of protein a day and vit C
If you start having contractions, you can also take a bath with Epsom Salts, it will help you to relax and get some Magnesium in your body.
Take Calcium supplement.
If you do these and have moderate activity ( no extreme overdoing, or working in extreme heat) and still have contractions on and off, braxton hiicksl then just take it as your body slowly starting to get ready for your birth. It can be totally normal!