5 month baby is exauhsted.?

My son is 5 months, has been put on zantac because in the middle of the night he would stop breathing, choke on his muscus and then apparently has acid reflux. He still coughs and all but lately, especially today, he has been sleeping. He will stay up for 45 minutes then pass out. I'm worried he might be sick. He is due for his second round of shots. He eats more than the baby next door but hes not over weight. Could he be sick?