It would be much smarter to go back to the attorney who represented in court. This is not an easy process so you should maximize your efforts by having an experienced criminal defense attorney.
Technically the answer is yes you can file your own papers. However, when defendants file pro se the petition usually just gets filed and never given a court date because in Philadelphia after the motion is filed it must be brought to the judge for a court date.
John M Walsh, Esquire
2101 Pine St
Philadelphia, PA 19103