I hadn't heard from you in so long that I had to go back and read your initial post, which also tells me that, if you're still having a problem, maybe you need to try to change some things. First of all, your lo may need even thicker liquids. If you're doing nectar, try honey and if you can, try to have a modified barium swallow test completed. If you are still having trouble this test is absolutely warranted at this point. I absolutely understand how you feel, Luke was always a big baby too and so to the Dr's it wasn't too worrisome, but to anyone who fed him, well, we were about to lose our minds.
If your lo is 4 mos., go ahead and introduce some solids, for 2 reasons. One, because he isn't get as much calories from food, this will help (though you still need help to get him to take the bottle) and two, if he's a formula baby, they often do start solids at 4 mos. What you need to do though, is just skip stage 1 foods and go to stage 2 foods. Stage 2 is already thicker which helps, however, some are still runny (e.g. peaches) and you will still want to thicken them either with rice cereal or with a powdered liquid thickener from the drug store. They are able to better control solids coming from the spoon, however, once they mix with saliva, they become thinner and they can have some difficulty. It should be a really smooth process though as long as you thicken them up a little bit.
Please feel free to vent! I totally understand the frustration and anxiety this can cause! Ufortunately, I'll be out of town from Thurs-Sun, but if you have more questions, I"ll try to get back to you ASAP! Good luck and hang in there!