I am about to turn 27 and I am about 2.5 years into my PhD program. I am in science and I am somewhat of a special case because I am in a special accredited stream for the field in which I plan to specialize. This stream is basically a standard PhD, but with a heavy course load. So far I have completed 8 full term (4 month) courses and I'm currently finishing another 2. I have achieved excellent marks in all of these classes.
I have been struggling with my research project. It involves some difficult mathematical modeling in which my supervisor is an expert. In fact, my supervisor is a super star researcher in his early 60's who works long hours and manages a lab of around 15 people, meaning he is always extremely busy. He has not shied away from expressing his displeasure with this accredited stream I am in, as the heavy course load has gotten in the way of research some times. Just this week I had to reschedule an experiment because I had a midterm the following day and realized I simply had too much material to review. Knowing how he feels about it, I find that I feel constant guilt for even being in this stream and for every time I have to prioritize course work over my research.
My project itself has been frustrating in the sense that when I run into problems or challenges, I simply don't have the necessary experience with this modeling to know how to address it. I have tried anyway, but with little success. When I consult him for advice, he will usually give me an idea of what to try, or most often he is unsure and doesn't have the time to look into it. This causes me to hit a brick wall, and then he will put me onto another path. The end result is that now I have a ton of ground work done for about 5 different projects and in each of them there is some problem preventing me from moving forward.
He recently expressed concern about my progress given that I am 2.5 years in and have "little worthwhile" to show. I have had periods during this program where I have been guilty of procrastination or lack of motivation. But this week I felt I got re-motivated to really tackle my modeling project and I sent him some results via email (he's out of town for 2 weeks.) His response indicated that there was an issue with the data and his tone made me feel completely useless. He even ended the email with "I am surprised you are not aware of this????" After reading this I am completely demoralized. I am constantly worried about my research and feel as though I lack the necessary skills to progress. For the first time, thoughts of just quitting are running through my mind. My supervisor's previous students have had the reputation of taking very long to finish. (4 years for a masters, 2 PhD students that each took 8 years, another that took 7 years...) I feel like I am headed toward this, and the thought of doing another 6 years of this makes me extremely depressed.
I don't really want to quit, given that I know this will lead to the job I want and I don't have a good alternative plan, but I am sick of feeling useless in this project, and I am sick of being made to feel like an idiot when I consult my supervisor.
Any advice?