He made his Championship debut for Watford against Scunthorpe United on 23 October 2010 as a late substitute, and again came on at half time in the match against Derby County on 30 October 2010, scoring his first professional goal within ten minutes. Whichelow featured for Watford 17 more times during the 2010/11 season, which included 4 starts and 2 goals. Having missed most of pre-season for Watford, Whichelow joined Exeter City on loan on 16 September 2011 for a month to gain match fitness.
He was however loaned out again, this time to Wycombe Wanderers on a one-month youth loan deal on 31 January 2012.
He scored on his debut against Tranmere Rovers. Whichelow was then loaned to League Two club Accrington Stanley on a months loan in September 2012.
His loan was extended into a second and third month, where he made a total of 4 appearances. He returned to parent club Watford on 20 December.
On 4 February 2013, Watford confirmed that Whichelow had been released by mutual consent.
He spent the last few months of the 2012-2013 season training with Forest Green Rovers and in July 2013 spent time on trial with Braintree Town. He joined Boreham Wood in August 2013. On 16 October 2015, Whichelow joined Chelmsford City on a three-month loan deal.
Whichelow scored twice on his debut for Chelmsford City in a 1–2 victory away at Basingstoke Town.