Difficulty feeding?

My baby is 6 months old and for the past 10 days has been taking in less milk. She is formula fed as my supply was too low for her as from birth- before this started she was guzzling bottles all day. She’s been started on bits of solids because of the reduced milk. When she had the bottle placed to her mouth she will either accept and drink between 3-4oz or she won’t take it in her mouth at all. She purses her lips and turns away her head. I took her to see the gp today who diagnosed her with a viral infection presumably a cold and a congested throat slightly on one side. She also said she suspects she’s teething. Yesterday she had 18oz and from since this has started that’s the least she’s taken. Today she’s had around 19oz and a few sooons of prunes as she seems to be struggling passing wind and a bowel movement.

She’s had Calpol, bonjella, saline spray, nurofen and nothing seems to make her drink as she used too.

She was previously sleeping 7pm-8am without any night feeds but now has started waking several times with gas, coughing or just waking for no cause I can see.

She doesn’t take milk when she wakes at night often and it she does it’s the same as usual in the day. Will take 3-4oz and turn her head away purses lips.

Is it common for this to affect feeding for so many days? I’m very worried and losing sleep with comforting her and settling her as well as worrying about her. Her temp, ears, mouth everything is fine. What can I do. Doctor said stuck to Calpol but it’s not making a difference. Many times I have to feed her laying flat as this is the only way she will take it. Any advice