Yes, it sounds like your PCP is listening to you. At 2.5/day you're taking 17.5 mg/week (which seems like a pretty small dosage). Increasing it to the current dosage you indicated raises it to 22.5 - it's more than 20% higher, so if you weren't already running so low, even this increase could be questionable. It seems like a good start, but I agree with others that you probably shouldn't have to wait two weeks to see how the new dosing works (except that you DO want to see the results of those 5 mg doses after they've had a chance to work).
Your PCP prescribing warfarin 100 at a time is a good idea - I don't know if your insurance pays for 100 pills at a time -- if not, there are pharmacies that will sell 90 generic Warfarin for $10. This approach is an alternative that you may want to consider - it may even be better than your insurance co-pay (assuming, of course, that you're fortunate enough to have insurance).
2.5 is an interesting dosage because you can create many different dosages (all multiples of 1.25) from them. If you need 7.5, it's three pills - 3.75 is 1 1/2 pills, etc. When you and your doctor get a handle on your dosing, it may make more sense at that time to add pills of different dosages to your dosing arsenal - perhaps a 2 (that can be broken into 1s if needed), perhaps a 5 (just to save money if you NEED a 5 and don't want to waste an extra 2.5 mg pill to make 5).
Your diet and increasing activity probably WILL produce changes in your INR -- you may want to monitor these more frequently than every other week -- especially because your INR is already pretty low and if you start eating greens that contain high levels of Vitamin K, the combination may push your INRs dangerously low.
When you (or your insurance) can afford it, getting your own meter, so you don't have to wait for others to say they want you to come in, can reduce a lot of the insecurity about your ACTUAL INR. Being able to test at home (or wherever) is an empowering feeling. (I can't and won't recommend it, but I bought my meter on eBay and am confident in its accuracy - even after comparing a result to a hospital lab. There are quite a few meters out there, and not all are extremely expensive. But, of course, this is up to you).