Suggest Remedies For Severe Vomiting In An Infant

Question : My son is 11 months old. As a daily routine, last night he had cerelac at about 9.30 PM, was breast-fed for 3-4 minutes and slept at about 10.15 PM. We also gave him Ultra-D3 drops and Mucolite drops(as he was having slight congestion) after he had cerelac.
Then at about 11.45 he had vomitting while sleeping and it seemed to me that he was not able to digest cerelac as it came out along with some mucus. Then he was breast-fed after 10 minutes, that too he was not able to digest and vomitted again after few minutes. We somehow made him sleep that time, later at about 3 AM, when he was breast-fed again, he vomitted again after few minutes. All the three times, when he vomitted, we can see some mucus coming out.
Then it was at around 5.30 AM when he was crying a bit, and when he was breast-fed, he was all good. Then till 4 PM, he was breast-fed several times in a day, along with XXXXXXX milk (as usual), meshed banana, and khichdi (in liquid form). He was able to digest all these things whole day without any problem.
Then at about 6 PM, we gave him khichdi (in liquid form) again, and then he was breast-fed at around 6.45 PM. Within 5-10 minutes, he vomitted again and khichdi came out. I didn't notice any mucus this time.
He passed motion 2 times, which was normal. He is active as usual and didn't had any fever.
What could be the possible reasons for this ? Is there anything to worry about ?

Thanks,
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