"This was the fourth time my action was questioned and I had nearly quit the game," said Ahmed, who was reported after the opening Test against England at Multan last week.
Ahmed, 29, was playing his first Test after being cleared by the ICC in October.
His action was questioned for a third time in the West Indies in May this year and he was subsequently banned from bowling at international level after undergoing tests in July.
The Pakistan Cricket Board withdrew Ahmed from the remaining two Tests against England, saying the paceman would take further remedial measures in Australia next month.
Ahmed described the whole issue as confusing.
"I am confused because I was cleared just last month and it is frustrating for me," said Ahmed, who equalled Waqar Younis's Pakistani record of fastest 50 wickets in the Test at Multan.
He now has so far grabbed 51 wickets in 10 Tests.
Pakistan coach Bob Woolmer also criticised the ICC's process of dealing with bowlers with illegal actions, saying it needed a review.
"A bowler is cleared after tests, bowls for the first time and is reported again. The process is not satisfactory and needs to be looked at," said Woolmer.
Ahmed was first reported during a tri-series in Sharjah in 1998 and then in 2004 during his team's tour of New Zealand. He now faces a one-year ban if found transgressing the ICC limits for bowlers.
Under the new ICC rules, all bowlers are allowed to straighten their bowling arms by 15 degrees.