The local rental market is HOT right now and nice houses at fair prices are going pretty quickly. How your place stacks up to the rest in the same area/condition/going rental price is the major factor as to how quickly you are going to find a renter. How soon is quick? Sometimes its a matter of days and sometimes weeks--3 weeks is not wholly unreasonable depending on the facts at hand--especially considering you just finished the improvements a week ago. How many showings have you had since the improvements were made? If it's only been up for a week in the improved condition and new price, that doesn't sound unreasonable at all. How long is your listing contract? How long did your agent intially estimate your market time would be--and at what price? If the home is being marketed in the local real estate system (MLS) and you are getting showings and offers it sounds like your agent is--at the very least--doing a significant and crucial part their job. If, however, negotiations are mishandled (by the owner or the agent), that could squash a deal that would otherwise sail through.
But, before you start blaming anyone, you need to thoroughly dissect why the two offers stalled, and what is going on with the marketing (including internet activity on Trulia and Zillow), the number of showings, recent local comparable closed transactions (time on market and price), the comparable condition of the property, and above all--the price. Do you have an open line of communication available with your agent? After all this data is examined a pretty clear picture as to why the home isn't moving should become pretty clear. Good luck!