My 3 month old baby

Is sick...he has a runny nose and had a fever I’m pretty sure of 100.9 maybe a little more he wouldn’t let me take his temperature but after feeding him...(I breast feed and supplement with formula) his temperature went down a bit, his head and chest were pretty hot. I took most of his clothes off and just kept him in a long sleeve onesie and socks. His temperature would go up and down a bit but I couldn’t take him to the ER. My husband works all day and I left the baby’s car seat base in my husbands car. Once my husband got home baby was still fussy and warm but I figured if his temperature goes up well take him to the ER. I don’t know if I’m doing the right thing....baby won’t sleep too much but he’s trying to I keep touching his chest, back and his head to make sure he’s not burning up. Can I do anything else? I don’t want to give him Tylenol unless his doctor tells me it’s ok but I don’t want him to be in any pain...I feel so bad and useless. What can I do????