I would like to offer a few comments and tips
1. Sanding styrene and resin: Although polystyrene is considered a low-toxicity material, there is some indication that it can cause some inflammatory activity in the lung dependent on the surface area of the particulate. Resin dust is simply a nuisance particulate, that, like any dust, can irritate the respiratory system--dependent on its concentration in air, frequency and duration of exposure, and any personal susceptibilities (ie, asthma).
Tip: The best thing you can do is to wet sand these products. Keeping your plastic and resin wet can reduce or almost eliminate any airborne particulates generated during sanding.
2. Super glues: Cyanoacrylates have been known to cause allergic reactions (chemical asthma) in some individuals after repeated exposures. MicroSol and Future don't evaporate very fast, so it takes more time to get much (if any) airborne vapor concentrations.
Tip: Keep your nose out of the jar. I have a terrible habit of getting very close to my work, and sometimes I think I inhale as much as goes on the part to be worked. Put a small fan slightly behind you and to the side, blowing toward your work. The airflow will dilute vapor concentrations, and carry them out of your breathing zone. In addition, try to back away when applying or working with solvents. Use a magnifier of some sort to help keep your distance. Keeping an open window will also help by allowing an exhchange of fresh air. Furthermore, keep the lid on your containers, and move them away from your immediate work area when not in use. Lastly, keep your room and work area(s) clean and free of dust. And don't sit with a trash can between your legs that's full of solvent-contaminated paper towels, etc.
3. The materials that you and I used 30 years ago are still around, but many have been reformulated to make them more "environmentally friendly". Notice I didn't say safer. Big difference, although having said that, many solvents have been substituted with other, "safer" solvents that require a higher dose over similar exposure times to produce the same effect. What that means is that your hobby glue now contains MEK, and it takes almost 4 times the amount to get you as "high" as toluene did, and without the reproductive health effects. Enamel and lacquer paints are not the only kids on the block anymore. Many modelers now choose to paint with acrylic enamels, which are "relatively" safer (alcohols and glycol ethers can still cause problems).
Tip: Use only the amount to get the job done. Go with liquid instead of the thick tube glue. Instead of using the brush that comes with liquid glue, use a No. 1 round paint brush (or smaller). See no. 2 above.
If following a few of these guidelines doesn't help eliminate the need for a respirator while you are building (as opposed to painting), then I would echo Mr. Lafleche's directives: Make an appointment to see your doctor, and go over your symptoms with him. Be sure to include the types of materials you are using, the amounts you use, and how often you use them. Our bodies change over time (how well I know!), and things that didn't affect us years ago, do now.
Let us know how things go, and all the best to you.
Gip Winecoff