Hello,
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Look you joined a gym just a week ago not a year ago. So 1st month your muscles gets relaxed and sets according they need to growth. After completing 3 months you will see the changes of Growing muscle's if you on natural Diet.  If you want results within 3 months, you better take supplements with a proper instructions. Without instructions they are harmful.
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And coming to biceps they need proper concentrated workout and a proper diet biceps take longer and longer time to form. So, 3 to 5 months they take to look with a proper results. Need to wait and work till. Have patience