You should not use a 'to'-infinitive in this sentence.
'To'-infinitives only follow certain verbs, and while 'help' is one of them, this is a different use of the word.
To explain - in the sentence "I got help to buy my house", 'help' means support or assistance.
But in sentences like "I could not help it", 'help' is defined as "stop yourself". For example, these essentially mean the same:
I could not help but laugh.
I could not stop myself from laughing.
"I can't help but..." is a particular idiom that draws meaning from this secondary use of 'help', and uses the conjunction 'but' to introduce something that happened contrary to your best efforts to stop yourself.