The commonest cause for this is usually colic OR uncomfortable room temperature or clothing. Hunger could be another cause. At this age,give 2 solid meals a day including curd and Banana in the diet in addition to whatever you prepare at home,the second feed being just before his sleep time at night. Give 4 milk feeds including one top formula feed using a spoon and katori and rest breastfeeding. Make sure that the bedroom is cool and comfortable,as is his clothing. Keep him close to you,separation anxiety starts setting around this age!!