I filed and had my tax return accepted January 29th 2019. It is now April 3rd 2019, why have I still not recieved my return and why is it still being processed?

Only the IRS controls when and if a Federal tax refund is Approved and Issued.

The dates for receiving a tax refund after it has been accepted by the IRS are only estimates based on the IRS target of issuing a tax refund after 21 days from the date it was accepted by the IRS.  This is a target only and not a guarantee.

After the tax return has been Accepted by the IRS (meaning only that they received the return) it will be in the Processing mode until the tax refund has been Approved and then an Issue Date will be available on the IRS website.

See this IRS website for federal tax refund FAQ's - https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions

Call the IRS:  1-800-829-1040  hours 7 AM - 7 PM local time Monday-Friday